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<html><head><meta http-equiv="content-type" content="text/html; charset=utf-8"/><title>2 High-level interface</title><link rel="stylesheet" type="text/css" href="scribble.css" title="default"/><link rel="stylesheet" type="text/css" href="racket.css" title="default"/><link rel="stylesheet" type="text/css" href="footnote.css" title="default"/><link rel="stylesheet" type="text/css" href="manual-style.css" title="default"/><link rel="stylesheet" type="text/css" href="manual-racket.css" title="default"/><script type="text/javascript" src="scribble-common.js"></script><!--[if IE 6]><style type="text/css">.SIEHidden { overflow: hidden; }</style><![endif]--></head><body id="scribble-racket-lang-org"><div class="tocset"><div class="tocview"><div class="tocviewlist tocviewlisttopspace"><div class="tocviewtitle"><table cellspacing="0" cellpadding="0"><tr><td style="width: 1em;"><a href="javascript:void(0);" title="Expand/Collapse" class="tocviewtoggle" onclick="TocviewToggle(this,"tocview_0");">▼</a></td><td></td><td><a href="index.html" class="tocviewlink" data-pltdoc="x">Marketplace:<span class="mywbr"> </span> Network-<wbr></wbr>Aware Programming</a></td></tr></table></div><div class="tocviewsublisttop" style="display: block;" id="tocview_0"><table cellspacing="0" cellpadding="0"><tr><td align="right">1 </td><td><a href="Concepts.html" class="tocviewlink" data-pltdoc="x">Concepts</a></td></tr><tr><td align="right">2 </td><td><a href="high-level-interface.html" class="tocviewselflink" data-pltdoc="x">High-<wbr></wbr>level interface</a></td></tr><tr><td align="right">3 </td><td><a href="low-level-interface.html" class="tocviewlink" data-pltdoc="x">Low-<wbr></wbr>level interface</a></td></tr><tr><td align="right">4 </td><td><a href="Drivers.html" class="tocviewlink" data-pltdoc="x">Drivers</a></td></tr><tr><td align="right">5 </td><td><a href="Management_and_Monitoring.html" class="tocviewlink" data-pltdoc="x">Management and Monitoring</a></td></tr><tr><td align="right">6 </td><td><a href="Examples.html" class="tocviewlink" data-pltdoc="x">Examples</a></td></tr></table></div></div><div class="tocviewlist"><table cellspacing="0" cellpadding="0"><tr><td style="width: 1em;"><a href="javascript:void(0);" title="Expand/Collapse" class="tocviewtoggle" onclick="TocviewToggle(this,"tocview_1");">►</a></td><td>2 </td><td><a href="high-level-interface.html" class="tocviewselflink" data-pltdoc="x">High-<wbr></wbr>level interface</a></td></tr></table><div class="tocviewsublistbottom" style="display: none;" id="tocview_1"><table cellspacing="0" cellpadding="0"><tr><td align="right">2.1 </td><td><a href="high-level-interface.html#%28part._hashlang-variations%29" class="tocviewlink" data-pltdoc="x">Using <span class="stt">#lang marketplace</span> and friends</a></td></tr><tr><td align="right">2.2 </td><td><a href="high-level-interface.html#%28part._.Using_.Marketplace_as_a_library%29" class="tocviewlink" data-pltdoc="x">Using Marketplace as a library</a></td></tr><tr><td align="right">2.3 </td><td><a href="high-level-interface.html#%28part._constructing-transitions%29" class="tocviewlink" data-pltdoc="x">Constructing transitions</a></td></tr><tr><td align="right">2.4 </td><td><a href="high-level-interface.html#%28part._endpoint-dsl%29" class="tocviewlink" data-pltdoc="x">Creating endpoints</a></td></tr><tr><td align="right">2.5 </td><td><a href="high-level-interface.html#%28part._deleting-endpoints%29" class="tocviewlink" data-pltdoc="x">Deleting endpoints</a></td></tr><tr><td align="right">2.6 </td><td><a href="high-level-interface.html#%28part._.Sending_messages_and_feedback%29" class="tocviewlink" data-pltdoc="x">Sending messages and feedback</a></td></tr><tr><td align="right">2.7 </td><td><a href="high-level-interface.html#%28part._.Creating_processes%29" class="tocviewlink" data-pltdoc="x">Creating processes</a></td></tr><tr><td align="right">2.8 </td><td><a href="high-level-interface.html#%28part._.Exiting_and_killing_processes%29" class="tocviewlink" data-pltdoc="x">Exiting and killing processes</a></td></tr><tr><td align="right">2.9 </td><td><a href="high-level-interface.html#%28part._.Cooperative_scheduling%29" class="tocviewlink" data-pltdoc="x">Cooperative scheduling</a></td></tr><tr><td align="right">2.10 </td><td><a href="high-level-interface.html#%28part._.Creating_nested_.V.Ms%29" class="tocviewlink" data-pltdoc="x">Creating nested VMs</a></td></tr><tr><td align="right">2.11 </td><td><a href="high-level-interface.html#%28part._.Relaying_across_layers%29" class="tocviewlink" data-pltdoc="x">Relaying across layers</a></td></tr></table></div></div></div><div class="tocsub"><div class="tocsubtitle">On this page:</div><table class="tocsublist" cellspacing="0"><tr><td><span class="tocsublinknumber">2.1<tt> </tt></span><a href="#%28part._hashlang-variations%29" class="tocsubseclink" data-pltdoc="x">Using <span class="stt">#lang marketplace</span> and friends</a></td></tr><tr><td><span class="tocsublinknumber">2.2<tt> </tt></span><a href="#%28part._.Using_.Marketplace_as_a_library%29" class="tocsubseclink" data-pltdoc="x">Using Marketplace as a library</a></td></tr><tr><td><a href="#%28form._%28%28lib._marketplace%2Fsugar-untyped..rkt%29._ground-vm%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktStxLink">ground-<wbr></wbr>vm</span></span></a></td></tr><tr><td><a href="#%28form._%28%28lib._marketplace%2Fsugar-typed..rkt%29._ground-vm~3a%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktStxLink">ground-<wbr></wbr>vm:</span></span></a></td></tr><tr><td><span class="tocsublinknumber">2.3<tt> </tt></span><a href="#%28part._constructing-transitions%29" class="tocsubseclink" data-pltdoc="x">Constructing transitions</a></td></tr><tr><td><a href="#%28form._%28%28lib._marketplace%2Fsugar-values..rkt%29._transition%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktStxLink">transition</span></span></a></td></tr><tr><td><a href="#%28form._%28%28lib._marketplace%2Fsugar-typed..rkt%29._transition~3a%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktStxLink">transition:</span></span></a></td></tr><tr><td><a href="#%28form._%28%28lib._marketplace%2Fsugar-typed..rkt%29._transition%2Fno-state%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktStxLink">transition/<span class="mywbr"> </span>no-<wbr></wbr>state</span></span></a></td></tr><tr><td><a href="#%28def._%28%28lib._marketplace%2Fsugar-values..rkt%29._transition%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktStxLink">transition</span></span></a></td></tr><tr><td><a href="#%28def._%28%28lib._marketplace%2Fmain..rkt%29._.Transition%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktValLink">Transition</span></span></a></td></tr><tr><td><a href="#%28def._%28%28lib._marketplace%2Fmain..rkt%29._.Action.Tree%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktValLink">Action<span class="mywbr"> </span>Tree</span></span></a></td></tr><tr><td><a href="#%28def._%28%28lib._marketplace%2Fmain..rkt%29._.Constreeof%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktValLink">Constreeof</span></span></a></td></tr><tr><td><a href="#%28def._%28%28lib._marketplace%2Fsugar-values..rkt%29._sequence-actions%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktValLink">sequence-<wbr></wbr>actions</span></span></a></td></tr><tr><td><span class="tocsublinknumber">2.4<tt> </tt></span><a href="#%28part._endpoint-dsl%29" class="tocsubseclink" data-pltdoc="x">Creating endpoints</a></td></tr><tr><td><a href="#%28form._%28%28lib._marketplace%2Fsugar-untyped..rkt%29._publisher%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktStxLink">publisher</span></span></a></td></tr><tr><td><a href="#%28form._%28%28lib._marketplace%2Fsugar-typed..rkt%29._publisher~3a%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktStxLink">publisher:</span></span></a></td></tr><tr><td><a href="#%28form._%28%28lib._marketplace%2Fsugar-untyped..rkt%29._subscriber%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktStxLink">subscriber</span></span></a></td></tr><tr><td><a href="#%28form._%28%28lib._marketplace%2Fsugar-typed..rkt%29._subscriber~3a%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktStxLink">subscriber:</span></span></a></td></tr><tr><td><a href="#%28form._%28%28lib._marketplace%2Fsugar-untyped..rkt%29._observe-subscribers%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktStxLink">observe-<wbr></wbr>subscribers</span></span></a></td></tr><tr><td><a href="#%28form._%28%28lib._marketplace%2Fsugar-typed..rkt%29._observe-subscribers~3a%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktStxLink">observe-<wbr></wbr>subscribers:</span></span></a></td></tr><tr><td><a href="#%28form._%28%28lib._marketplace%2Fsugar-untyped..rkt%29._observe-publishers%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktStxLink">observe-<wbr></wbr>publishers</span></span></a></td></tr><tr><td><a href="#%28form._%28%28lib._marketplace%2Fsugar-typed..rkt%29._observe-publishers~3a%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktStxLink">observe-<wbr></wbr>publishers:</span></span></a></td></tr><tr><td><a href="#%28form._%28%28lib._marketplace%2Fsugar-untyped..rkt%29._observe-subscribers%2Feverything%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktStxLink">observe-<wbr></wbr>subscribers/<span class="mywbr"> </span>everything</span></span></a></td></tr><tr><td><a href="#%28form._%28%28lib._marketplace%2Fsugar-typed..rkt%29._observe-subscribers%2Feverything~3a%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktStxLink">observe-<wbr></wbr>subscribers/<span class="mywbr"> </span>everything:</span></span></a></td></tr><tr><td><a href="#%28form._%28%28lib._marketplace%2Fsugar-untyped..rkt%29._observe-publishers%2Feverything%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktStxLink">observe-<wbr></wbr>publishers/<span class="mywbr"> </span>everything</span></span></a></td></tr><tr><td><a href="#%28form._%28%28lib._marketplace%2Fsugar-typed..rkt%29._observe-publishers%2Feverything~3a%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktStxLink">observe-<wbr></wbr>publishers/<span class="mywbr"> </span>everything:</span></span></a></td></tr><tr><td><a href="#%28form._%28%28lib._marketplace%2Fsugar-untyped..rkt%29._build-endpoint%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktStxLink">build-<wbr></wbr>endpoint</span></span></a></td></tr><tr><td><a href="#%28form._%28%28lib._marketplace%2Fsugar-typed..rkt%29._build-endpoint~3a%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktStxLink">build-<wbr></wbr>endpoint:</span></span></a></td></tr><tr><td><span class="tocsublinknumber">2.4.1<tt> </tt></span><a href="#%28part._.Receiving_messages%29" class="tocsubseclink" data-pltdoc="x">Receiving messages</a></td></tr><tr><td><a href="#%28form._%28%28lib._marketplace%2Fsugar-untyped..rkt%29._on-message%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktStxLink">on-<wbr></wbr>message</span></span></a></td></tr><tr><td><span class="tocsublinknumber">2.4.2<tt> </tt></span><a href="#%28part._.Action-only_vs__.State_updates%29" class="tocsubseclink" data-pltdoc="x">Action-<wbr></wbr>only vs. State updates</a></td></tr><tr><td><a href="#%28form._%28%28lib._marketplace%2Fsugar-untyped..rkt%29._match-state%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktStxLink">match-<wbr></wbr>state</span></span></a></td></tr><tr><td><span class="tocsublinknumber">2.4.3<tt> </tt></span><a href="#%28part._.Handling_presence_and_absence_events%29" class="tocsubseclink" data-pltdoc="x">Handling presence and absence events</a></td></tr><tr><td><a href="#%28form._%28%28lib._marketplace%2Fsugar-untyped..rkt%29._on-presence%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktStxLink">on-<wbr></wbr>presence</span></span></a></td></tr><tr><td><a href="#%28form._%28%28lib._marketplace%2Fsugar-untyped..rkt%29._on-absence%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktStxLink">on-<wbr></wbr>absence</span></span></a></td></tr><tr><td><span class="tocsublinknumber">2.4.4<tt> </tt></span><a href="#%28part._.Exit_reasons%29" class="tocsubseclink" data-pltdoc="x">Exit reasons</a></td></tr><tr><td><a href="#%28form._%28%28lib._marketplace%2Fsugar-untyped..rkt%29._match-reason%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktStxLink">match-<wbr></wbr>reason</span></span></a></td></tr><tr><td><span class="tocsublinknumber">2.4.5<tt> </tt></span><a href="#%28part._updating-endpoints%29" class="tocsubseclink" data-pltdoc="x">Updating endpoints</a></td></tr><tr><td><span class="tocsublinknumber">2.4.6<tt> </tt></span><a href="#%28part._.Who_am_.I_talking_to_%29" class="tocsubseclink" data-pltdoc="x">Who am I talking to?</a></td></tr><tr><td><a href="#%28form._%28%28lib._marketplace%2Fsugar-untyped..rkt%29._match-orientation%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktStxLink">match-<wbr></wbr>orientation</span></span></a></td></tr><tr><td><a href="#%28form._%28%28lib._marketplace%2Fsugar-untyped..rkt%29._match-conversation%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktStxLink">match-<wbr></wbr>conversation</span></span></a></td></tr><tr><td><a href="#%28form._%28%28lib._marketplace%2Fsugar-untyped..rkt%29._match-interest-type%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktStxLink">match-<wbr></wbr>interest-<wbr></wbr>type</span></span></a></td></tr><tr><td><span class="tocsublinknumber">2.4.7<tt> </tt></span><a href="#%28part._participating-vs-observing%29" class="tocsubseclink" data-pltdoc="x">Participating in a conversation vs. observing conversations</a></td></tr><tr><td><span class="tocsublinknumber">2.4.8<tt> </tt></span><a href="#%28part._naming-endpoints%29" class="tocsubseclink" data-pltdoc="x">Naming endpoints</a></td></tr><tr><td><a href="#%28def._%28%28lib._marketplace%2Fsugar-typed..rkt%29._name-endpoint%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktValLink">name-<wbr></wbr>endpoint</span></span></a></td></tr><tr><td><a href="#%28form._%28%28lib._marketplace%2Fsugar-untyped..rkt%29._let-fresh%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktStxLink">let-<wbr></wbr>fresh</span></span></a></td></tr><tr><td><span class="tocsublinknumber">2.5<tt> </tt></span><a href="#%28part._deleting-endpoints%29" class="tocsubseclink" data-pltdoc="x">Deleting endpoints</a></td></tr><tr><td><a href="#%28def._%28%28lib._marketplace%2Fsugar-values..rkt%29._delete-endpoint%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktValLink">delete-<wbr></wbr>endpoint</span></span></a></td></tr><tr><td><span class="tocsublinknumber">2.6<tt> </tt></span><a href="#%28part._.Sending_messages_and_feedback%29" class="tocsubseclink" data-pltdoc="x">Sending messages and feedback</a></td></tr><tr><td><a href="#%28def._%28%28lib._marketplace%2Fsugar-values..rkt%29._send-message%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktValLink">send-<wbr></wbr>message</span></span></a></td></tr><tr><td><a href="#%28def._%28%28lib._marketplace%2Fsugar-values..rkt%29._send-feedback%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktValLink">send-<wbr></wbr>feedback</span></span></a></td></tr><tr><td><span class="tocsublinknumber">2.7<tt> </tt></span><a href="#%28part._.Creating_processes%29" class="tocsubseclink" data-pltdoc="x">Creating processes</a></td></tr><tr><td><a href="#%28form._%28%28lib._marketplace%2Fsugar-untyped..rkt%29._spawn%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktStxLink">spawn</span></span></a></td></tr><tr><td><a href="#%28form._%28%28lib._marketplace%2Fsugar-untyped..rkt%29._spawn%2Fcontinue%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktStxLink">spawn/<span class="mywbr"> </span>continue</span></span></a></td></tr><tr><td><a href="#%28form._%28%28lib._marketplace%2Fsugar-typed..rkt%29._spawn~3a%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktStxLink">spawn:</span></span></a></td></tr><tr><td><a href="#%28form._%28%28lib._marketplace%2Fsugar-typed..rkt%29._spawn%2Fcontinue~3a%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktStxLink">spawn/<span class="mywbr"> </span>continue:</span></span></a></td></tr><tr><td><a href="#%28def._%28%28lib._marketplace%2Fsugar-typed..rkt%29._name-process%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktValLink">name-<wbr></wbr>process</span></span></a></td></tr><tr><td><span class="tocsublinknumber">2.8<tt> </tt></span><a href="#%28part._.Exiting_and_killing_processes%29" class="tocsubseclink" data-pltdoc="x">Exiting and killing processes</a></td></tr><tr><td><a href="#%28def._%28%28lib._marketplace%2Fsugar-values..rkt%29._quit%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktValLink">quit</span></span></a></td></tr><tr><td><span class="tocsublinknumber">2.9<tt> </tt></span><a href="#%28part._.Cooperative_scheduling%29" class="tocsubseclink" data-pltdoc="x">Cooperative scheduling</a></td></tr><tr><td><a href="#%28form._%28%28lib._marketplace%2Fsugar-untyped..rkt%29._yield%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktStxLink">yield</span></span></a></td></tr><tr><td><a href="#%28form._%28%28lib._marketplace%2Fsugar-typed..rkt%29._yield~3a%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktStxLink">yield:</span></span></a></td></tr><tr><td><span class="tocsublinknumber">2.10<tt> </tt></span><a href="#%28part._.Creating_nested_.V.Ms%29" class="tocsubseclink" data-pltdoc="x">Creating nested VMs</a></td></tr><tr><td><a href="#%28form._%28%28lib._marketplace%2Fsugar-untyped..rkt%29._spawn-vm%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktStxLink">spawn-<wbr></wbr>vm</span></span></a></td></tr><tr><td><a href="#%28form._%28%28lib._marketplace%2Fsugar-typed..rkt%29._spawn-vm~3a%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktStxLink">spawn-<wbr></wbr>vm:</span></span></a></td></tr><tr><td><span class="tocsublinknumber">2.11<tt> </tt></span><a href="#%28part._.Relaying_across_layers%29" class="tocsubseclink" data-pltdoc="x">Relaying across layers</a></td></tr><tr><td><a href="#%28form._%28%28lib._marketplace%2Fsugar-typed..rkt%29._at-meta-level~3a%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktStxLink">at-<wbr></wbr>meta-<wbr></wbr>level:</span></span></a></td></tr><tr><td><a href="#%28def._%28%28lib._marketplace%2Fsugar-untyped..rkt%29._at-meta-level%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktValLink">at-<wbr></wbr>meta-<wbr></wbr>level</span></span></a></td></tr></table></div></div><div class="maincolumn"><div class="main"><div class="versionbox"><span class="version">6.0.0.1</span></div><div class="navsettop"><span class="navleft"> </span><span class="navright"> <a href="Concepts.html" title="backward to "1 Concepts"" data-pltdoc="x">← prev</a> <a href="index.html" title="up to "Marketplace: Network-Aware Programming"" data-pltdoc="x">up</a> <a href="low-level-interface.html" title="forward to "3 Low-level interface"" data-pltdoc="x">next →</a></span> </div><h3>2<tt> </tt><a name="(part._high-level-interface)"></a>High-level interface</h3><p>This high-level interface between a VM and a process is analogous to
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the <span style="font-style: italic">C library interface</span> of a Unix-like operating system. The
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<a href="low-level-interface.html" data-pltdoc="x">Low-level interface</a> corresponds to the <span style="font-style: italic">system call
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interface</span> of a Unix-like operating system.</p><h4>2.1<tt> </tt><a name="(part._hashlang-variations)"></a><a name="(mod-path._marketplace)"></a>Using <span class="stt">#lang marketplace</span> and friends</h4><p><table cellspacing="0" class="defmodule"><tr><td align="left"><span class="hspace"> </span><a href="http://docs.racket-lang.org/guide/Module_Syntax.html#%28part._hash-lang%29" class="RktModLink" data-pltdoc="x"><span class="RktMod">#lang</span></a><span class="hspace"> </span><a href="high-level-interface.html#%28mod-path._marketplace%29" class="RktModLink" data-pltdoc="x"><span class="RktSym">marketplace</span></a></td><td align="right"><span class="RpackageSpec"><span class="Smaller"> package:</span> <span class="stt">marketplace</span></span></td></tr></table></p><p>Programs written for Marketplace differ from normal Racket modules
|
|
only in their selection of language. A Racket module written with
|
|
<span class="stt">#lang marketplace</span>, such as the echo server in
|
|
<a href="Examples.html#%28part._echo-server-example%29" data-pltdoc="x">TCP echo server</a>, specifies a sequence of definitions
|
|
and startup <a href="Concepts.html#%28tech._action%29" class="techoutside" data-pltdoc="x"><span class="techinside">actions</span></a> for an application. Typically, initial
|
|
actions spawn application processes and nested VMs, which in turn
|
|
subscribe to sources of events from the outside world.</p><p>At present, there’s just <span class="stt">#lang marketplace</span>. In future, there will
|
|
be a variation for Typed Racket, and languages providing greater
|
|
support for flow control, responsibility transfer, and other
|
|
networking concepts. For now, Typed Racket programs must be written as
|
|
<span class="stt">#lang typed/racket</span> programs using <span class="RktPn">(</span><span class="RktSym"><a href="http://docs.racket-lang.org/reference/require.html#%28form._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._require%29%29" class="RktStxLink" data-pltdoc="x">require</a></span><span class="stt"> </span><span class="RktSym">marketplace</span><span class="RktPn">)</span>
|
|
and <span class="RktSym"><a href="high-level-interface.html#%28form._%28%28lib._marketplace%2Fsugar-typed..rkt%29._ground-vm~3a%29%29" class="RktStxLink" data-pltdoc="x">ground-vm:</a></span> explicitly.</p><h4>2.2<tt> </tt><a name="(part._.Using_.Marketplace_as_a_library)"></a><a name="(mod-path._marketplace/sugar-untyped)"></a><a name="(mod-path._marketplace/sugar-typed)"></a>Using Marketplace as a library</h4><p><table cellspacing="0" class="defmodule"><tr><td align="left" colspan="2"><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="http://docs.racket-lang.org/reference/require.html#%28form._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._require%29%29" class="RktStxLink" data-pltdoc="x">require</a></span><span class="stt"> </span><a href="high-level-interface.html#%28mod-path._marketplace%2Fsugar-untyped%29" class="RktModLink" data-pltdoc="x"><span class="RktSym">marketplace/sugar-untyped</span></a><span class="RktPn">)</span></td></tr><tr><td align="left" colspan="2"><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="http://docs.racket-lang.org/reference/require.html#%28form._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._require%29%29" class="RktStxLink" data-pltdoc="x">require</a></span><span class="stt"> </span><a href="high-level-interface.html#%28mod-path._marketplace%2Fsugar-typed%29" class="RktModLink" data-pltdoc="x"><span class="RktSym">marketplace/sugar-typed</span></a><span class="RktPn">)</span></td></tr><tr><td align="left"> </td><td align="right"><span class="RpackageSpec"><span class="Smaller"> package:</span> <span class="stt">marketplace</span></span></td></tr></table></p><p>Instead of using Racket’s <span class="stt">#lang</span> feature, ordinary Racket programs
|
|
can use Marketplace features by requiring Marketplace modules
|
|
directly.</p><p>Such programs need to use <span class="RktSym"><a href="high-level-interface.html#%28form._%28%28lib._marketplace%2Fsugar-untyped..rkt%29._ground-vm%29%29" class="RktStxLink" data-pltdoc="x">ground-vm</a></span>/<span class="RktSym"><a href="high-level-interface.html#%28form._%28%28lib._marketplace%2Fsugar-typed..rkt%29._ground-vm~3a%29%29" class="RktStxLink" data-pltdoc="x">ground-vm:</a></span> to
|
|
start the ground-level VM explicitly. They also need to explicitly
|
|
start any drivers they need; for example, the file
|
|
<span class="stt">"examples/echo-plain.rkt"</span> uses <span class="RktSym"><a href="high-level-interface.html#%28form._%28%28lib._marketplace%2Fsugar-untyped..rkt%29._ground-vm%29%29" class="RktStxLink" data-pltdoc="x">ground-vm</a></span> along with
|
|
<span class="RktSym"><a href="Drivers.html#%28def._%28%28lib._marketplace%2Fdrivers%2Ftcp-bare..rkt%29._tcp%29%29" class="RktValLink" data-pltdoc="x">tcp</a></span> and an initial <span class="RktSym">endpoint</span> action:</p><blockquote class="SCodeFlow"><table cellspacing="0" class="RktBlk"><tr><td><span class="RktPn">(</span><span class="RktSym"><a href="high-level-interface.html#%28form._%28%28lib._marketplace%2Fsugar-untyped..rkt%29._ground-vm%29%29" class="RktStxLink" data-pltdoc="x">ground-vm</a></span><span class="hspace"> </span><span class="RktSym"><a href="Drivers.html#%28def._%28%28lib._marketplace%2Fdrivers%2Ftcp-bare..rkt%29._tcp%29%29" class="RktValLink" data-pltdoc="x">tcp</a></span></td></tr><tr><td><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="high-level-interface.html#%28form._%28%28lib._marketplace%2Fsugar-untyped..rkt%29._subscriber%29%29" class="RktStxLink" data-pltdoc="x">subscriber</a></span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym">tcp-channel</span><span class="hspace"> </span><span class="RktSym"><a href="low-level-interface.html#%28def._%28%28lib._marketplace%2Fsugar-untyped..rkt%29._~3f%29%29" class="RktValLink" data-pltdoc="x">?</a></span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym">tcp-listener</span><span class="hspace"> </span><span class="RktVal">5999</span><span class="RktPn">)</span><span class="hspace"> </span><span class="RktSym"><a href="low-level-interface.html#%28def._%28%28lib._marketplace%2Fsugar-untyped..rkt%29._~3f%29%29" class="RktValLink" data-pltdoc="x">?</a></span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="high-level-interface.html#%28form._%28%28lib._marketplace%2Fsugar-untyped..rkt%29._match-conversation%29%29" class="RktStxLink" data-pltdoc="x">match-conversation</a></span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym">tcp-channel</span><span class="hspace"> </span><span class="RktSym">from</span><span class="hspace"> </span><span class="RktSym">to</span><span class="hspace"> </span><span class="RktSym"><a href="http://docs.racket-lang.org/reference/stx-patterns.html#%28form._%28%28lib._racket%2Fprivate%2Fstxcase-scheme..rkt%29.__%29%29" class="RktStxLink" data-pltdoc="x">_</a></span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="high-level-interface.html#%28form._%28%28lib._marketplace%2Fsugar-untyped..rkt%29._on-presence%29%29" class="RktStxLink" data-pltdoc="x">on-presence</a></span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="high-level-interface.html#%28form._%28%28lib._marketplace%2Fsugar-untyped..rkt%29._spawn%29%29" class="RktStxLink" data-pltdoc="x">spawn</a></span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym">echoer</span><span class="hspace"> </span><span class="RktSym">from</span><span class="hspace"> </span><span class="RktSym">to</span><span class="RktPn">)</span><span class="RktPn">)</span><span class="RktPn">)</span><span class="RktPn">)</span><span class="RktPn">)</span><span class="RktPn">)</span></td></tr></table></blockquote><p><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" class="boxed RBoxed"><tr><td><table cellspacing="0" class="together"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>syntax</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(form._((lib._marketplace/sugar-untyped..rkt)._ground-vm))"></a><span title="Provided from: marketplace/sugar-untyped, marketplace/sugar-typed"><span class="RktSym"><a href="high-level-interface.html#%28form._%28%28lib._marketplace%2Fsugar-untyped..rkt%29._ground-vm%29%29" class="RktStxDef RktStxLink" data-pltdoc="x">ground-vm</a></span></span><span class="hspace"> </span><span class="RktVar">maybe-boot-pid-binding</span><span class="hspace"> </span><span class="RktVar">maybe-initial-state</span><span class="hspace"> </span><span class="RktVar">initial-action</span><span class="hspace"> </span><span class="RktMeta">...</span><span class="RktPn">)</span></p></blockquote></td></tr></table></td></tr><tr><td><table cellspacing="0" class="together"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>syntax</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(form._((lib._marketplace/sugar-typed..rkt)._ground-vm~3a))"></a><span title="Provided from: marketplace/sugar-untyped, marketplace/sugar-typed"><span class="RktSym"><a href="high-level-interface.html#%28form._%28%28lib._marketplace%2Fsugar-typed..rkt%29._ground-vm~3a%29%29" class="RktStxDef RktStxLink" data-pltdoc="x">ground-vm:</a></span></span><span class="hspace"> </span><span class="RktVar">maybe-boot-pid-binding</span><span class="hspace"> </span><span class="RktVar">maybe-typed-initial-state</span><span class="hspace"> </span><span class="RktVar">initial-action</span><span class="hspace"> </span><span class="RktMeta">...</span><span class="RktPn">)</span></p></blockquote></td></tr><tr><td><span class="stt"> </span></td></tr><tr><td><table cellspacing="0" class="specgrammar"><tr><td align="right" valign="baseline"><span class="RktVar">maybe-boot-pid-binding</span></td><td align="left" valign="baseline"><span class="stt"> </span></td><td align="center" valign="baseline">=</td><td align="left" valign="baseline"><span class="stt"> </span></td><td align="left" valign="baseline"><table cellspacing="0" class="RktBlk"><tr><td></td></tr></table></td></tr><tr><td align="right" valign="baseline"><span class="stt"> </span></td><td align="left" valign="baseline"><span class="stt"> </span></td><td align="center" valign="baseline">|</td><td align="left" valign="baseline"><span class="stt"> </span></td><td align="left" valign="baseline"><span class="RktPn">#:boot-pid</span><span class="hspace"> </span><span class="RktVar">id</span></td></tr><tr><td align="right" valign="baseline"><span class="stt"> </span></td><td align="left" valign="baseline"><span class="stt"> </span></td><td align="center" valign="baseline"><span class="stt"> </span></td><td align="left" valign="baseline"><span class="stt"> </span></td><td align="left" valign="baseline"><span class="stt"> </span></td></tr><tr><td align="right" valign="baseline"><span class="RktVar">maybe-initial-state</span></td><td align="left" valign="baseline"><span class="stt"> </span></td><td align="center" valign="baseline">=</td><td align="left" valign="baseline"><span class="stt"> </span></td><td align="left" valign="baseline"><table cellspacing="0" class="RktBlk"><tr><td></td></tr></table></td></tr><tr><td align="right" valign="baseline"><span class="stt"> </span></td><td align="left" valign="baseline"><span class="stt"> </span></td><td align="center" valign="baseline">|</td><td align="left" valign="baseline"><span class="stt"> </span></td><td align="left" valign="baseline"><span class="RktPn">#:initial-state</span><span class="hspace"> </span><span class="RktVar">expr</span></td></tr><tr><td align="right" valign="baseline"><span class="stt"> </span></td><td align="left" valign="baseline"><span class="stt"> </span></td><td align="center" valign="baseline"><span class="stt"> </span></td><td align="left" valign="baseline"><span class="stt"> </span></td><td align="left" valign="baseline"><span class="stt"> </span></td></tr><tr><td align="right" valign="baseline"><span class="RktVar">maybe-typed-initial-state</span></td><td align="left" valign="baseline"><span class="stt"> </span></td><td align="center" valign="baseline">=</td><td align="left" valign="baseline"><span class="stt"> </span></td><td align="left" valign="baseline"><table cellspacing="0" class="RktBlk"><tr><td></td></tr></table></td></tr><tr><td align="right" valign="baseline"><span class="stt"> </span></td><td align="left" valign="baseline"><span class="stt"> </span></td><td align="center" valign="baseline">|</td><td align="left" valign="baseline"><span class="stt"> </span></td><td align="left" valign="baseline"><span class="RktPn">#:initial-state</span><span class="hspace"> </span><span class="RktVar">expr</span><span class="hspace"> </span><span class="RktVar">:</span><span class="hspace"> </span><span class="RktVar">type</span></td></tr><tr><td align="right" valign="baseline"><span class="stt"> </span></td><td align="left" valign="baseline"><span class="stt"> </span></td><td align="center" valign="baseline"><span class="stt"> </span></td><td align="left" valign="baseline"><span class="stt"> </span></td><td align="left" valign="baseline"><span class="stt"> </span></td></tr><tr><td align="right" valign="baseline"><span class="RktVar">initial-action</span></td><td align="left" valign="baseline"><span class="stt"> </span></td><td align="center" valign="baseline">=</td><td align="left" valign="baseline"><span class="stt"> </span></td><td align="left" valign="baseline"><span class="RktVar">expr</span></td></tr></table></td></tr></table></td></tr></table></blockquote></div><div class="SIntrapara">Starts the ground VM, in untyped and typed programs, respectively. If
|
|
<span class="RktPn">#:boot-pid</span> is specified, the given identifier is bound within
|
|
the form to the PID of the <span style="font-style: italic">primordial process</span> that performs the
|
|
initial actions. If <span class="RktPn">#:initial-state</span> is specified (with a
|
|
type, for <span class="RktSym"><a href="high-level-interface.html#%28form._%28%28lib._marketplace%2Fsugar-typed..rkt%29._ground-vm~3a%29%29" class="RktStxLink" data-pltdoc="x">ground-vm:</a></span>), it is used as the initial state for
|
|
the primordial process; if it is not supplied, the primordial process
|
|
is given <span class="RktPn">(</span><span class="RktSym"><a href="http://docs.racket-lang.org/reference/void.html#%28def._%28%28quote._~23~25kernel%29._void%29%29" class="RktValLink" data-pltdoc="x">void</a></span><span class="RktPn">)</span> as its initial state (and <span class="RktSym"><a href="http://docs.racket-lang.org/ts-reference/type-ref.html#%28form._%28%28lib._typed-racket%2Fbase-env%2Fbase-types..rkt%29._.Void%29%29" class="RktStxLink" data-pltdoc="x">Void</a></span> as
|
|
its state type).</div></p><h4>2.3<tt> </tt><a name="(part._constructing-transitions)"></a>Constructing transitions</h4><p><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" class="boxed RBoxed"><tr><td><table cellspacing="0" class="together"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>syntax</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(form._((lib._marketplace/sugar-values..rkt)._transition))"></a><span class="RktSym"><a href="high-level-interface.html#%28form._%28%28lib._marketplace%2Fsugar-values..rkt%29._transition%29%29" class="RktStxDef RktStxLink" data-pltdoc="x">transition</a></span><span class="hspace"> </span><span class="RktVar">new-state</span><span class="hspace"> </span><span class="RktVar">action-tree</span><span class="hspace"> </span><span class="RktMeta">...</span><span class="RktPn">)</span></p></blockquote></td></tr></table></td></tr><tr><td><table cellspacing="0" class="together"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>syntax</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(form._((lib._marketplace/sugar-typed..rkt)._transition~3a))"></a><span class="RktSym"><a href="high-level-interface.html#%28form._%28%28lib._marketplace%2Fsugar-typed..rkt%29._transition~3a%29%29" class="RktStxDef RktStxLink" data-pltdoc="x">transition:</a></span><span class="hspace"> </span><span class="RktVar">new-state</span><span class="hspace"> </span><span class="RktVar">:</span><span class="hspace"> </span><span class="RktVar">State</span><span class="hspace"> </span><span class="RktVar">action-tree</span><span class="hspace"> </span><span class="RktMeta">...</span><span class="RktPn">)</span></p></blockquote></td></tr></table></td></tr><tr><td><table cellspacing="0" class="together"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>syntax</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(form._((lib._marketplace/sugar-typed..rkt)._transition/no-state))"></a><span class="RktSym"><a href="high-level-interface.html#%28form._%28%28lib._marketplace%2Fsugar-typed..rkt%29._transition%2Fno-state%29%29" class="RktStxDef RktStxLink" data-pltdoc="x">transition/no-state</a></span><span class="hspace"> </span><span class="RktVar">action-tree</span><span class="hspace"> </span><span class="RktMeta">...</span><span class="RktPn">)</span></p></blockquote></td></tr></table></td></tr></table></blockquote></div><div class="SIntrapara">Each of these forms produces a <span class="RktSym"><a href="high-level-interface.html#%28def._%28%28lib._marketplace%2Fmain..rkt%29._.Transition%29%29" class="RktValLink" data-pltdoc="x">Transition</a></span> structure. The
|
|
first is for untyped code, the second for typed code (where the
|
|
mandatory <span class="RktVar">State</span> is the type of the transitioning process’s
|
|
private state), and the third for either.</div></p><p>Each <span class="RktVar">action-tree</span> must be an <span class="RktPn">(</span><span class="RktSym"><a href="high-level-interface.html#%28def._%28%28lib._marketplace%2Fmain..rkt%29._.Action.Tree%29%29" class="RktValLink" data-pltdoc="x">ActionTree</a></span><span class="stt"> </span><span class="RktVar">State</span><span class="RktPn">)</span>.</p><p>It’s fine to include <span style="font-style: italic">no</span> action-trees, in which case the
|
|
transition merely updates the state of the process without taking any
|
|
actions.</p><p>In the case of <span class="RktSym"><a href="high-level-interface.html#%28form._%28%28lib._marketplace%2Fsugar-typed..rkt%29._transition%2Fno-state%29%29" class="RktStxLink" data-pltdoc="x">transition/no-state</a></span>, the type <span class="RktSym"><a href="http://docs.racket-lang.org/ts-reference/type-ref.html#%28form._%28%28lib._typed-racket%2Fbase-env%2Fbase-types..rkt%29._.Void%29%29" class="RktStxLink" data-pltdoc="x">Void</a></span>
|
|
and value <span class="RktPn">(</span><span class="RktSym"><a href="http://docs.racket-lang.org/reference/void.html#%28def._%28%28quote._~23~25kernel%29._void%29%29" class="RktValLink" data-pltdoc="x">void</a></span><span class="RktPn">)</span> is used for the process state.
|
|
<span class="RktSym"><a href="high-level-interface.html#%28form._%28%28lib._marketplace%2Fsugar-typed..rkt%29._transition%2Fno-state%29%29" class="RktStxLink" data-pltdoc="x">transition/no-state</a></span> is useful for processes that are
|
|
stateless other than the implicit state of their endpoints.</p><p><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" class="boxed RBoxed"><tr><td><table cellspacing="0" class="together"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>struct</p></div></div><table cellspacing="0" class="RForeground"><tr><td><span class="RktPn">(</span><span class="RktSym"><a href="http://docs.racket-lang.org/reference/define-struct.html#%28form._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._struct%29%29" class="RktStxLink" data-pltdoc="x">struct</a></span></td><td><span class="hspace"> </span></td><td><a name="(def._((lib._marketplace/main..rkt)._transition-actions))"></a><a name="(def._((lib._marketplace/main..rkt)._transition-state))"></a><a name="(def._((lib._marketplace/main..rkt)._transition~3f))"></a><a name="(def._((lib._marketplace/main..rkt)._struct~3atransition))"></a><a name="(def._((lib._marketplace/sugar-values..rkt)._transition))"></a><span class="RktSym"><a href="high-level-interface.html#%28form._%28%28lib._marketplace%2Fsugar-values..rkt%29._transition%29%29" class="RktStxDef RktStxLink" data-pltdoc="x">transition</a></span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym">state</span><span class="stt"> </span><span class="RktSym">actions</span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace"> </span></td><td><span class="hspace"> </span></td><td><span class="RktPn">#:transparent</span><span class="RktPn">)</span></td></tr></table></blockquote></td></tr><tr><td><span class="hspace"> </span><span class="RktSym">state</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym">State</span></td></tr><tr><td><span class="hspace"> </span><span class="RktSym">actions</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="high-level-interface.html#%28def._%28%28lib._marketplace%2Fmain..rkt%29._.Action.Tree%29%29" class="RktValLink" data-pltdoc="x">ActionTree</a></span><span class="hspace"> </span><span class="RktSym">State</span><span class="RktPn">)</span></td></tr></table></td></tr><tr><td><table cellspacing="0" class="together"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>type</p></div></div><p class="RForeground"><a name="(def._((lib._marketplace/main..rkt)._.Transition))"></a><span class="RktSym"><a href="high-level-interface.html#%28def._%28%28lib._marketplace%2Fmain..rkt%29._.Transition%29%29" class="RktValDef RktValLink" data-pltdoc="x">Transition</a></span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="http://docs.racket-lang.org/ts-reference/type-ref.html#%28form._%28%28lib._typed-racket%2Fbase-env%2Fbase-types-extra..rkt%29._.All%29%29" class="RktStxLink" data-pltdoc="x">All</a></span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym">State</span><span class="RktPn">)</span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="high-level-interface.html#%28form._%28%28lib._marketplace%2Fsugar-values..rkt%29._transition%29%29" class="RktStxLink" data-pltdoc="x">transition</a></span><span class="hspace"> </span><span class="RktSym">State</span><span class="RktPn">)</span><span class="RktPn">)</span></p></blockquote></td></tr></table></td></tr></table></blockquote></div><div class="SIntrapara">A transition structure. The <span class="RktSym"><a href="high-level-interface.html#%28def._%28%28lib._marketplace%2Fmain..rkt%29._transition-state%29%29" class="RktValLink" data-pltdoc="x">transition-state</a></span> field is the new
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private state the process will have after the transition is applied,
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and the <span class="RktSym"><a href="high-level-interface.html#%28def._%28%28lib._marketplace%2Fmain..rkt%29._transition-actions%29%29" class="RktValLink" data-pltdoc="x">transition-actions</a></span> are the actions that will be
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performed by the VM in order to apply the transition.</div></p><p><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" class="boxed RBoxed"><tr><td><table cellspacing="0" class="together"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>type</p></div></div><p class="RForeground"><a name="(def._((lib._marketplace/main..rkt)._.Action.Tree))"></a><span class="RktSym"><a href="high-level-interface.html#%28def._%28%28lib._marketplace%2Fmain..rkt%29._.Action.Tree%29%29" class="RktValDef RktValLink" data-pltdoc="x">ActionTree</a></span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="http://docs.racket-lang.org/ts-reference/type-ref.html#%28form._%28%28lib._typed-racket%2Fbase-env%2Fbase-types-extra..rkt%29._.All%29%29" class="RktStxLink" data-pltdoc="x">All</a></span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym">State</span><span class="RktPn">)</span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="high-level-interface.html#%28def._%28%28lib._marketplace%2Fmain..rkt%29._.Constreeof%29%29" class="RktValLink" data-pltdoc="x">Constreeof</a></span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="low-level-interface.html#%28def._%28%28lib._marketplace%2Fmain..rkt%29._.Action%29%29" class="RktValLink" data-pltdoc="x">Action</a></span><span class="hspace"> </span><span class="RktSym">State</span><span class="RktPn">)</span><span class="RktPn">)</span><span class="RktPn">)</span></p></blockquote></td></tr></table></td></tr><tr><td><table cellspacing="0" class="together"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>type</p></div></div><p class="RForeground"><a name="(def._((lib._marketplace/main..rkt)._.Constreeof))"></a><span class="RktSym"><a href="high-level-interface.html#%28def._%28%28lib._marketplace%2Fmain..rkt%29._.Constreeof%29%29" class="RktValDef RktValLink" data-pltdoc="x">Constreeof</a></span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="http://docs.racket-lang.org/ts-reference/type-ref.html#%28form._%28%28lib._typed-racket%2Fbase-env%2Fbase-types-extra..rkt%29._.All%29%29" class="RktStxLink" data-pltdoc="x">All</a></span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym">X</span><span class="RktPn">)</span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="http://docs.racket-lang.org/ts-reference/type-ref.html#%28form._%28%28lib._typed-racket%2Fbase-env%2Fbase-types-extra..rkt%29._.Rec%29%29" class="RktStxLink" data-pltdoc="x">Rec</a></span><span class="hspace"> </span><span class="RktSym">CT</span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="http://docs.racket-lang.org/ts-reference/type-ref.html#%28form._%28%28lib._typed-racket%2Fbase-env%2Fbase-types-extra..rkt%29._.U%29%29" class="RktStxLink" data-pltdoc="x">U</a></span><span class="hspace"> </span><span class="RktSym">X</span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="http://docs.racket-lang.org/ts-reference/type-ref.html#%28form._%28%28lib._typed-racket%2Fbase-env%2Fbase-types..rkt%29._.Pairof%29%29" class="RktStxLink" data-pltdoc="x">Pairof</a></span><span class="hspace"> </span><span class="RktSym">CT</span><span class="hspace"> </span><span class="RktSym">CT</span><span class="RktPn">)</span><span class="hspace"> </span><span class="RktSym"><a href="http://docs.racket-lang.org/ts-reference/type-ref.html#%28form._%28%28lib._typed-racket%2Fbase-env%2Fbase-types..rkt%29._.False%29%29" class="RktStxLink" data-pltdoc="x">False</a></span><span class="hspace"> </span><span class="RktSym"><a href="http://docs.racket-lang.org/ts-reference/type-ref.html#%28form._%28%28lib._typed-racket%2Fbase-env%2Fbase-types..rkt%29._.Void%29%29" class="RktStxLink" data-pltdoc="x">Void</a></span><span class="hspace"> </span><span class="RktSym"><a href="http://docs.racket-lang.org/ts-reference/type-ref.html#%28form._%28%28lib._typed-racket%2Fbase-env%2Fbase-types..rkt%29._.Null%29%29" class="RktStxLink" data-pltdoc="x">Null</a></span><span class="RktPn">)</span><span class="RktPn">)</span><span class="RktPn">)</span></p></blockquote></td></tr></table></td></tr></table></blockquote></div><div class="SIntrapara">An action-tree is a <a name="(tech._cons._tree)"></a><span style="font-style: italic">cons-tree</span> of <span class="RktSym"><a href="low-level-interface.html#%28def._%28%28lib._marketplace%2Fmain..rkt%29._.Action%29%29" class="RktValLink" data-pltdoc="x">Action</a></span>s. When
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performing actions, a VM will traverse an action-tree in left-to-right
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order.</div></p><p><span class="RktVal">'</span><span class="RktVal">(</span><span class="RktVal">)</span>, <span class="RktPn">(</span><span class="RktSym"><a href="http://docs.racket-lang.org/reference/void.html#%28def._%28%28quote._~23~25kernel%29._void%29%29" class="RktValLink" data-pltdoc="x">void</a></span><span class="RktPn">)</span>, and <span class="RktVal">#f</span> may also be present in
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action-trees: when the VM reaches such a value, it ignores it and
|
|
continues with the next leaf in the tree.</p><p>For example, all of the following are valid action trees which will
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send messages <span class="RktVal">1</span>, <span class="RktVal">2</span> and <span class="RktVal">3</span> in that order:</p><blockquote class="SCodeFlow"><table cellspacing="0" class="RktBlk"><tr><td><span class="RktPn">(</span><span class="RktSym"><a href="http://docs.racket-lang.org/reference/pairs.html#%28def._%28%28quote._~23~25kernel%29._list%29%29" class="RktValLink" data-pltdoc="x">list</a></span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="high-level-interface.html#%28def._%28%28lib._marketplace%2Fsugar-values..rkt%29._send-message%29%29" class="RktValLink" data-pltdoc="x">send-message</a></span><span class="hspace"> </span><span class="RktVal">1</span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="high-level-interface.html#%28def._%28%28lib._marketplace%2Fsugar-values..rkt%29._send-message%29%29" class="RktValLink" data-pltdoc="x">send-message</a></span><span class="hspace"> </span><span class="RktVal">2</span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="high-level-interface.html#%28def._%28%28lib._marketplace%2Fsugar-values..rkt%29._send-message%29%29" class="RktValLink" data-pltdoc="x">send-message</a></span><span class="hspace"> </span><span class="RktVal">3</span><span class="RktPn">)</span><span class="RktPn">)</span></td></tr></table></blockquote><blockquote class="SCodeFlow"><table cellspacing="0" class="RktBlk"><tr><td><span class="RktPn">(</span><span class="RktSym"><a href="http://docs.racket-lang.org/reference/pairs.html#%28def._%28%28quote._~23~25kernel%29._list%29%29" class="RktValLink" data-pltdoc="x">list</a></span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="http://docs.racket-lang.org/reference/pairs.html#%28def._%28%28quote._~23~25kernel%29._list%29%29" class="RktValLink" data-pltdoc="x">list</a></span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="high-level-interface.html#%28def._%28%28lib._marketplace%2Fsugar-values..rkt%29._send-message%29%29" class="RktValLink" data-pltdoc="x">send-message</a></span><span class="hspace"> </span><span class="RktVal">1</span><span class="RktPn">)</span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="http://docs.racket-lang.org/reference/pairs.html#%28def._%28%28quote._~23~25kernel%29._cons%29%29" class="RktValLink" data-pltdoc="x">cons</a></span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="high-level-interface.html#%28def._%28%28lib._marketplace%2Fsugar-values..rkt%29._send-message%29%29" class="RktValLink" data-pltdoc="x">send-message</a></span><span class="hspace"> </span><span class="RktVal">2</span><span class="RktPn">)</span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="http://docs.racket-lang.org/reference/pairs.html#%28def._%28%28quote._~23~25kernel%29._cons%29%29" class="RktValLink" data-pltdoc="x">cons</a></span><span class="hspace"> </span><span class="RktVal">'</span><span class="RktVal">(</span><span class="RktVal">)</span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="high-level-interface.html#%28def._%28%28lib._marketplace%2Fsugar-values..rkt%29._send-message%29%29" class="RktValLink" data-pltdoc="x">send-message</a></span><span class="hspace"> </span><span class="RktVal">3</span><span class="RktPn">)</span><span class="RktPn">)</span><span class="RktPn">)</span><span class="RktPn">)</span></td></tr></table></blockquote><blockquote class="SCodeFlow"><table cellspacing="0" class="RktBlk"><tr><td><span class="RktPn">(</span><span class="RktSym"><a href="http://docs.racket-lang.org/reference/pairs.html#%28def._%28%28quote._~23~25kernel%29._cons%29%29" class="RktValLink" data-pltdoc="x">cons</a></span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="http://docs.racket-lang.org/reference/pairs.html#%28def._%28%28quote._~23~25kernel%29._cons%29%29" class="RktValLink" data-pltdoc="x">cons</a></span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="high-level-interface.html#%28def._%28%28lib._marketplace%2Fsugar-values..rkt%29._send-message%29%29" class="RktValLink" data-pltdoc="x">send-message</a></span><span class="hspace"> </span><span class="RktVal">1</span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="high-level-interface.html#%28def._%28%28lib._marketplace%2Fsugar-values..rkt%29._send-message%29%29" class="RktValLink" data-pltdoc="x">send-message</a></span><span class="hspace"> </span><span class="RktVal">2</span><span class="RktPn">)</span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="http://docs.racket-lang.org/reference/pairs.html#%28def._%28%28quote._~23~25kernel%29._list%29%29" class="RktValLink" data-pltdoc="x">list</a></span><span class="hspace"> </span><span class="RktVal">#f</span><span class="hspace"> </span><span class="RktVal">#f</span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="high-level-interface.html#%28def._%28%28lib._marketplace%2Fsugar-values..rkt%29._send-message%29%29" class="RktValLink" data-pltdoc="x">send-message</a></span><span class="hspace"> </span><span class="RktVal">3</span><span class="RktPn">)</span><span class="RktPn">)</span><span class="RktPn">)</span></td></tr></table></blockquote><p>Because <span class="RktVal">#f</span> and <span class="RktPn">(</span><span class="RktSym"><a href="http://docs.racket-lang.org/reference/void.html#%28def._%28%28quote._~23~25kernel%29._void%29%29" class="RktValLink" data-pltdoc="x">void</a></span><span class="RktPn">)</span> are valid, ignored, members of
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an action-tree, <span class="RktSym"><a href="http://docs.racket-lang.org/reference/if.html#%28form._%28%28lib._racket%2Fprivate%2Fletstx-scheme..rkt%29._and%29%29" class="RktStxLink" data-pltdoc="x">and</a></span> and <span class="RktSym"><a href="http://docs.racket-lang.org/reference/when_unless.html#%28form._%28%28lib._racket%2Fprivate%2Fletstx-scheme..rkt%29._when%29%29" class="RktStxLink" data-pltdoc="x">when</a></span> can be used to
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selectively include actions in an action-tree:</p><blockquote class="SCodeFlow"><table cellspacing="0" class="RktBlk"><tr><td><span class="RktPn">(</span><span class="RktSym"><a href="http://docs.racket-lang.org/reference/pairs.html#%28def._%28%28quote._~23~25kernel%29._list%29%29" class="RktValLink" data-pltdoc="x">list</a></span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym">first-action</span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="http://docs.racket-lang.org/reference/when_unless.html#%28form._%28%28lib._racket%2Fprivate%2Fletstx-scheme..rkt%29._when%29%29" class="RktStxLink" data-pltdoc="x">when</a></span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym">condition?</span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym">optional-action</span><span class="RktPn">)</span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym">final-action</span><span class="RktPn">)</span><span class="RktPn">)</span></td></tr></table></blockquote><blockquote class="SCodeFlow"><table cellspacing="0" class="RktBlk"><tr><td><span class="RktPn">(</span><span class="RktSym"><a href="http://docs.racket-lang.org/reference/pairs.html#%28def._%28%28quote._~23~25kernel%29._list%29%29" class="RktValLink" data-pltdoc="x">list</a></span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym">first-action</span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="http://docs.racket-lang.org/reference/if.html#%28form._%28%28lib._racket%2Fprivate%2Fletstx-scheme..rkt%29._and%29%29" class="RktStxLink" data-pltdoc="x">and</a></span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym">condition?</span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym">optional-action</span><span class="RktPn">)</span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym">final-action</span><span class="RktPn">)</span><span class="RktPn">)</span></td></tr></table></blockquote><p>Finally, these inert placeholders can be used to represent "no action
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at all" in a transition:</p><blockquote class="SCodeFlow"><table cellspacing="0" class="RktBlk"><tr><td><span class="RktPn">(</span><span class="RktSym"><a href="high-level-interface.html#%28form._%28%28lib._marketplace%2Fsugar-values..rkt%29._transition%29%29" class="RktStxLink" data-pltdoc="x">transition</a></span><span class="hspace"> </span><span class="RktSym">new-state</span><span class="RktPn">)</span><span class="hspace"> </span><span class="RktCmt">;</span><span class="RktCmt"> </span><span class="RktCmt">No action-trees at all</span></td></tr><tr><td><span class="RktPn">(</span><span class="RktSym"><a href="high-level-interface.html#%28form._%28%28lib._marketplace%2Fsugar-values..rkt%29._transition%29%29" class="RktStxLink" data-pltdoc="x">transition</a></span><span class="hspace"> </span><span class="RktSym">new-state</span><span class="hspace"> </span><span class="RktVal">'</span><span class="RktVal">(</span><span class="RktVal">)</span><span class="RktPn">)</span></td></tr><tr><td><span class="RktPn">(</span><span class="RktSym"><a href="high-level-interface.html#%28form._%28%28lib._marketplace%2Fsugar-values..rkt%29._transition%29%29" class="RktStxLink" data-pltdoc="x">transition</a></span><span class="hspace"> </span><span class="RktSym">new-state</span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="http://docs.racket-lang.org/reference/void.html#%28def._%28%28quote._~23~25kernel%29._void%29%29" class="RktValLink" data-pltdoc="x">void</a></span><span class="RktPn">)</span><span class="RktPn">)</span></td></tr><tr><td><span class="RktPn">(</span><span class="RktSym"><a href="high-level-interface.html#%28form._%28%28lib._marketplace%2Fsugar-values..rkt%29._transition%29%29" class="RktStxLink" data-pltdoc="x">transition</a></span><span class="hspace"> </span><span class="RktSym">new-state</span><span class="hspace"> </span><span class="RktVal">#f</span><span class="RktPn">)</span></td></tr></table></blockquote><p><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>procedure</p></div></div><table cellspacing="0" class="prototype RForeground"><tr><td><span class="RktPn">(</span><a name="(def._((lib._marketplace/sugar-values..rkt)._sequence-actions))"></a><span class="RktSym"><a href="high-level-interface.html#%28def._%28%28lib._marketplace%2Fsugar-values..rkt%29._sequence-actions%29%29" class="RktValDef RktValLink" data-pltdoc="x">sequence-actions</a></span></td><td><span class="hspace"> </span></td><td><span class="RktVar">initial-transition</span></td><td><span class="hspace"> </span></td><td><span class="hspace"> </span></td><td><span class="hspace"> </span></td><td><span class="hspace"> </span></td></tr><tr><td><span class="hspace"> </span></td><td><span class="hspace"> </span></td><td><span class="RktVar">item</span><span class="hspace"> </span><span class="RktMeta">...</span><span class="RktPn">)</span></td><td><span class="hspace"> </span></td><td>→</td><td><span class="hspace"> </span></td><td><span class="RktPn">(</span><span class="RktSym"><a href="high-level-interface.html#%28def._%28%28lib._marketplace%2Fmain..rkt%29._.Transition%29%29" class="RktValLink" data-pltdoc="x">Transition</a></span><span class="hspace"> </span><span class="RktSym">State</span><span class="RktPn">)</span></td></tr></table></blockquote></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">initial-transition</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="high-level-interface.html#%28def._%28%28lib._marketplace%2Fmain..rkt%29._.Transition%29%29" class="RktValLink" data-pltdoc="x">Transition</a></span><span class="hspace"> </span><span class="RktSym">State</span><span class="RktPn">)</span></td></tr><tr><td><table cellspacing="0" class="argcontract"><tr><td><span class="hspace"> </span></td><td><span class="RktVar">item</span></td><td><span class="hspace"> </span></td><td>:</td><td><span class="hspace"> </span></td><td><table cellspacing="0" class="RktBlk"><tr><td><span class="RktPn">(</span><span class="RktSym"><a href="http://docs.racket-lang.org/ts-reference/type-ref.html#%28form._%28%28lib._typed-racket%2Fbase-env%2Fbase-types-extra..rkt%29._.U%29%29" class="RktStxLink" data-pltdoc="x">U</a></span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="high-level-interface.html#%28def._%28%28lib._marketplace%2Fmain..rkt%29._.Action.Tree%29%29" class="RktValLink" data-pltdoc="x">ActionTree</a></span><span class="hspace"> </span><span class="RktSym">State</span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym">State</span><span class="hspace"> </span><span class="RktSym"><a href="http://docs.racket-lang.org/ts-reference/type-ref.html#%28form._%28%28lib._typed-racket%2Fbase-env%2Fbase-types-extra..rkt%29._-~3e%29%29" class="RktStxLink" data-pltdoc="x"><span class="nobreak">-></span></a></span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="high-level-interface.html#%28def._%28%28lib._marketplace%2Fmain..rkt%29._.Transition%29%29" class="RktValLink" data-pltdoc="x">Transition</a></span><span class="hspace"> </span><span class="RktSym">State</span><span class="RktPn">)</span><span class="RktPn">)</span><span class="RktPn">)</span></td></tr></table></td></tr></table></td></tr></table></blockquote></div><div class="SIntrapara">Returns a transition formed from the <span class="RktVar">initial-transition</span>
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extended with new actions, possibly updating its carried state. Each
|
|
of the supplied <span class="RktVar">item</span>s is examined: if it is an
|
|
<span class="RktSym"><a href="high-level-interface.html#%28def._%28%28lib._marketplace%2Fmain..rkt%29._.Action.Tree%29%29" class="RktValLink" data-pltdoc="x">ActionTree</a></span>, it is appended to the pending transition’s
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actions; if it is a procedure, it is called with the <span style="font-style: italic">state</span> of
|
|
the pending transition, and is expected to return an updated
|
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transition.</div></p><p>For example,</p><blockquote class="SCodeFlow"><table cellspacing="0" class="RktBlk"><tr><td><span class="RktPn">(</span><span class="RktSym"><a href="high-level-interface.html#%28def._%28%28lib._marketplace%2Fsugar-values..rkt%29._sequence-actions%29%29" class="RktValLink" data-pltdoc="x">sequence-actions</a></span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="high-level-interface.html#%28form._%28%28lib._marketplace%2Fsugar-values..rkt%29._transition%29%29" class="RktStxLink" data-pltdoc="x">transition</a></span><span class="hspace"> </span><span class="RktVal">'</span><span class="RktVal">x</span></td></tr><tr><td><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="high-level-interface.html#%28def._%28%28lib._marketplace%2Fsugar-values..rkt%29._send-message%29%29" class="RktValLink" data-pltdoc="x">send-message</a></span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="http://docs.racket-lang.org/reference/pairs.html#%28def._%28%28quote._~23~25kernel%29._list%29%29" class="RktValLink" data-pltdoc="x">list</a></span><span class="hspace"> </span><span class="RktVal">'</span><span class="RktVal">message</span><span class="hspace"> </span><span class="RktVal">0</span><span class="RktPn">)</span><span class="RktPn">)</span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="high-level-interface.html#%28def._%28%28lib._marketplace%2Fsugar-values..rkt%29._send-message%29%29" class="RktValLink" data-pltdoc="x">send-message</a></span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="http://docs.racket-lang.org/reference/pairs.html#%28def._%28%28quote._~23~25kernel%29._list%29%29" class="RktValLink" data-pltdoc="x">list</a></span><span class="hspace"> </span><span class="RktVal">'</span><span class="RktVal">message</span><span class="hspace"> </span><span class="RktVal">1</span><span class="RktPn">)</span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="high-level-interface.html#%28def._%28%28lib._marketplace%2Fsugar-values..rkt%29._send-message%29%29" class="RktValLink" data-pltdoc="x">send-message</a></span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="http://docs.racket-lang.org/reference/pairs.html#%28def._%28%28quote._~23~25kernel%29._list%29%29" class="RktValLink" data-pltdoc="x">list</a></span><span class="hspace"> </span><span class="RktVal">'</span><span class="RktVal">message</span><span class="hspace"> </span><span class="RktVal">2</span><span class="RktPn">)</span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="http://docs.racket-lang.org/ts-reference/special-forms.html#%28form._%28%28lib._typed-racket%2Fbase-env%2Fprims..rkt%29._lambda%29%29" class="RktStxLink" data-pltdoc="x">lambda</a></span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym">old-state</span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="high-level-interface.html#%28form._%28%28lib._marketplace%2Fsugar-values..rkt%29._transition%29%29" class="RktStxLink" data-pltdoc="x">transition</a></span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="http://docs.racket-lang.org/reference/pairs.html#%28def._%28%28quote._~23~25kernel%29._cons%29%29" class="RktValLink" data-pltdoc="x">cons</a></span><span class="hspace"> </span><span class="RktVal">'</span><span class="RktVal">y</span><span class="hspace"> </span><span class="RktSym">old-state</span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="high-level-interface.html#%28def._%28%28lib._marketplace%2Fsugar-values..rkt%29._send-message%29%29" class="RktValLink" data-pltdoc="x">send-message</a></span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="http://docs.racket-lang.org/reference/pairs.html#%28def._%28%28quote._~23~25kernel%29._list%29%29" class="RktValLink" data-pltdoc="x">list</a></span><span class="hspace"> </span><span class="RktVal">'</span><span class="RktVal">message</span><span class="hspace"> </span><span class="RktVal">3</span><span class="RktPn">)</span><span class="RktPn">)</span><span class="RktPn">)</span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="high-level-interface.html#%28def._%28%28lib._marketplace%2Fsugar-values..rkt%29._send-message%29%29" class="RktValLink" data-pltdoc="x">send-message</a></span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="http://docs.racket-lang.org/reference/pairs.html#%28def._%28%28quote._~23~25kernel%29._list%29%29" class="RktValLink" data-pltdoc="x">list</a></span><span class="hspace"> </span><span class="RktVal">'</span><span class="RktVal">message</span><span class="hspace"> </span><span class="RktVal">4</span><span class="RktPn">)</span><span class="RktPn">)</span><span class="RktPn">)</span></td></tr></table></blockquote><p>produces the equivalent of</p><blockquote class="SCodeFlow"><table cellspacing="0" class="RktBlk"><tr><td><span class="RktPn">(</span><span class="RktSym"><a href="high-level-interface.html#%28form._%28%28lib._marketplace%2Fsugar-values..rkt%29._transition%29%29" class="RktStxLink" data-pltdoc="x">transition</a></span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="http://docs.racket-lang.org/reference/pairs.html#%28def._%28%28quote._~23~25kernel%29._cons%29%29" class="RktValLink" data-pltdoc="x">cons</a></span><span class="hspace"> </span><span class="RktVal">'</span><span class="RktVal">y</span><span class="hspace"> </span><span class="RktVal">'</span><span class="RktVal">x</span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="high-level-interface.html#%28def._%28%28lib._marketplace%2Fsugar-values..rkt%29._send-message%29%29" class="RktValLink" data-pltdoc="x">send-message</a></span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="http://docs.racket-lang.org/reference/pairs.html#%28def._%28%28quote._~23~25kernel%29._list%29%29" class="RktValLink" data-pltdoc="x">list</a></span><span class="hspace"> </span><span class="RktVal">'</span><span class="RktVal">message</span><span class="hspace"> </span><span class="RktVal">0</span><span class="RktPn">)</span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="high-level-interface.html#%28def._%28%28lib._marketplace%2Fsugar-values..rkt%29._send-message%29%29" class="RktValLink" data-pltdoc="x">send-message</a></span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="http://docs.racket-lang.org/reference/pairs.html#%28def._%28%28quote._~23~25kernel%29._list%29%29" class="RktValLink" data-pltdoc="x">list</a></span><span class="hspace"> </span><span class="RktVal">'</span><span class="RktVal">message</span><span class="hspace"> </span><span class="RktVal">1</span><span class="RktPn">)</span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="high-level-interface.html#%28def._%28%28lib._marketplace%2Fsugar-values..rkt%29._send-message%29%29" class="RktValLink" data-pltdoc="x">send-message</a></span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="http://docs.racket-lang.org/reference/pairs.html#%28def._%28%28quote._~23~25kernel%29._list%29%29" class="RktValLink" data-pltdoc="x">list</a></span><span class="hspace"> </span><span class="RktVal">'</span><span class="RktVal">message</span><span class="hspace"> </span><span class="RktVal">2</span><span class="RktPn">)</span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="high-level-interface.html#%28def._%28%28lib._marketplace%2Fsugar-values..rkt%29._send-message%29%29" class="RktValLink" data-pltdoc="x">send-message</a></span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="http://docs.racket-lang.org/reference/pairs.html#%28def._%28%28quote._~23~25kernel%29._list%29%29" class="RktValLink" data-pltdoc="x">list</a></span><span class="hspace"> </span><span class="RktVal">'</span><span class="RktVal">message</span><span class="hspace"> </span><span class="RktVal">3</span><span class="RktPn">)</span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="high-level-interface.html#%28def._%28%28lib._marketplace%2Fsugar-values..rkt%29._send-message%29%29" class="RktValLink" data-pltdoc="x">send-message</a></span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="http://docs.racket-lang.org/reference/pairs.html#%28def._%28%28quote._~23~25kernel%29._list%29%29" class="RktValLink" data-pltdoc="x">list</a></span><span class="hspace"> </span><span class="RktVal">'</span><span class="RktVal">message</span><span class="hspace"> </span><span class="RktVal">4</span><span class="RktPn">)</span><span class="RktPn">)</span><span class="RktPn">)</span></td></tr></table></blockquote><h4>2.4<tt> </tt><a name="(part._endpoint-dsl)"></a>Creating endpoints</h4><p>The primitive action that creates new endpoints is
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<span class="RktSym"><a href="low-level-interface.html#%28def._%28%28lib._marketplace%2Fmain..rkt%29._add-endpoint%29%29" class="RktValLink" data-pltdoc="x">add-endpoint</a></span>, but because endpoints are the most flexible and
|
|
complex point of interaction between a process and its VM, a
|
|
collection of macros helps streamline endpoint setup.</p><p><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" class="boxed RBoxed"><tr><td><table cellspacing="0" class="together"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>syntax</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(form._((lib._marketplace/sugar-untyped..rkt)._publisher))"></a><span class="RktSym"><a href="high-level-interface.html#%28form._%28%28lib._marketplace%2Fsugar-untyped..rkt%29._publisher%29%29" class="RktStxDef RktStxLink" data-pltdoc="x">publisher</a></span><span class="hspace"> </span><span class="RktVar">topic</span><span class="hspace"> </span><span class="RktVar">handler</span><span class="hspace"> </span><span class="RktMeta">...</span><span class="RktPn">)</span></p></blockquote></td></tr></table></td></tr><tr><td><table cellspacing="0" class="together"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>syntax</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(form._((lib._marketplace/sugar-typed..rkt)._publisher~3a))"></a><span class="RktSym"><a href="high-level-interface.html#%28form._%28%28lib._marketplace%2Fsugar-typed..rkt%29._publisher~3a%29%29" class="RktStxDef RktStxLink" data-pltdoc="x">publisher:</a></span><span class="hspace"> </span><span class="RktVar">State</span><span class="hspace"> </span><span class="RktVar">topic</span><span class="hspace"> </span><span class="RktVar">handler</span><span class="hspace"> </span><span class="RktMeta">...</span><span class="RktPn">)</span></p></blockquote></td></tr></table></td></tr><tr><td><table cellspacing="0" class="together"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>syntax</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(form._((lib._marketplace/sugar-untyped..rkt)._subscriber))"></a><span class="RktSym"><a href="high-level-interface.html#%28form._%28%28lib._marketplace%2Fsugar-untyped..rkt%29._subscriber%29%29" class="RktStxDef RktStxLink" data-pltdoc="x">subscriber</a></span><span class="hspace"> </span><span class="RktVar">topic</span><span class="hspace"> </span><span class="RktVar">handler</span><span class="hspace"> </span><span class="RktMeta">...</span><span class="RktPn">)</span></p></blockquote></td></tr></table></td></tr><tr><td><table cellspacing="0" class="together"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>syntax</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(form._((lib._marketplace/sugar-typed..rkt)._subscriber~3a))"></a><span class="RktSym"><a href="high-level-interface.html#%28form._%28%28lib._marketplace%2Fsugar-typed..rkt%29._subscriber~3a%29%29" class="RktStxDef RktStxLink" data-pltdoc="x">subscriber:</a></span><span class="hspace"> </span><span class="RktVar">State</span><span class="hspace"> </span><span class="RktVar">topic</span><span class="hspace"> </span><span class="RktVar">handler</span><span class="hspace"> </span><span class="RktMeta">...</span><span class="RktPn">)</span></p></blockquote></td></tr></table></td></tr><tr><td><table cellspacing="0" class="together"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>syntax</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(form._((lib._marketplace/sugar-untyped..rkt)._observe-subscribers))"></a><span class="RktSym"><a href="high-level-interface.html#%28form._%28%28lib._marketplace%2Fsugar-untyped..rkt%29._observe-subscribers%29%29" class="RktStxDef RktStxLink" data-pltdoc="x">observe-subscribers</a></span><span class="hspace"> </span><span class="RktVar">topic</span><span class="hspace"> </span><span class="RktVar">handler</span><span class="hspace"> </span><span class="RktMeta">...</span><span class="RktPn">)</span></p></blockquote></td></tr></table></td></tr><tr><td><table cellspacing="0" class="together"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>syntax</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(form._((lib._marketplace/sugar-typed..rkt)._observe-subscribers~3a))"></a><span class="RktSym"><a href="high-level-interface.html#%28form._%28%28lib._marketplace%2Fsugar-typed..rkt%29._observe-subscribers~3a%29%29" class="RktStxDef RktStxLink" data-pltdoc="x">observe-subscribers:</a></span><span class="hspace"> </span><span class="RktVar">State</span><span class="hspace"> </span><span class="RktVar">topic</span><span class="hspace"> </span><span class="RktVar">handler</span><span class="hspace"> </span><span class="RktMeta">...</span><span class="RktPn">)</span></p></blockquote></td></tr></table></td></tr><tr><td><table cellspacing="0" class="together"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>syntax</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(form._((lib._marketplace/sugar-untyped..rkt)._observe-publishers))"></a><span class="RktSym"><a href="high-level-interface.html#%28form._%28%28lib._marketplace%2Fsugar-untyped..rkt%29._observe-publishers%29%29" class="RktStxDef RktStxLink" data-pltdoc="x">observe-publishers</a></span><span class="hspace"> </span><span class="RktVar">topic</span><span class="hspace"> </span><span class="RktVar">handler</span><span class="hspace"> </span><span class="RktMeta">...</span><span class="RktPn">)</span></p></blockquote></td></tr></table></td></tr><tr><td><table cellspacing="0" class="together"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>syntax</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(form._((lib._marketplace/sugar-typed..rkt)._observe-publishers~3a))"></a><span class="RktSym"><a href="high-level-interface.html#%28form._%28%28lib._marketplace%2Fsugar-typed..rkt%29._observe-publishers~3a%29%29" class="RktStxDef RktStxLink" data-pltdoc="x">observe-publishers:</a></span><span class="hspace"> </span><span class="RktVar">State</span><span class="hspace"> </span><span class="RktVar">topic</span><span class="hspace"> </span><span class="RktVar">handler</span><span class="hspace"> </span><span class="RktMeta">...</span><span class="RktPn">)</span></p></blockquote></td></tr></table></td></tr><tr><td><table cellspacing="0" class="together"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>syntax</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(form._((lib._marketplace/sugar-untyped..rkt)._observe-subscribers/everything))"></a><span class="RktSym"><a href="high-level-interface.html#%28form._%28%28lib._marketplace%2Fsugar-untyped..rkt%29._observe-subscribers%2Feverything%29%29" class="RktStxDef RktStxLink" data-pltdoc="x">observe-subscribers/everything</a></span><span class="hspace"> </span><span class="RktVar">topic</span><span class="hspace"> </span><span class="RktVar">handler</span><span class="hspace"> </span><span class="RktMeta">...</span><span class="RktPn">)</span></p></blockquote></td></tr></table></td></tr><tr><td><table cellspacing="0" class="together"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>syntax</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(form._((lib._marketplace/sugar-typed..rkt)._observe-subscribers/everything~3a))"></a><span class="RktSym"><a href="high-level-interface.html#%28form._%28%28lib._marketplace%2Fsugar-typed..rkt%29._observe-subscribers%2Feverything~3a%29%29" class="RktStxDef RktStxLink" data-pltdoc="x">observe-subscribers/everything:</a></span><span class="hspace"> </span><span class="RktVar">State</span><span class="hspace"> </span><span class="RktVar">topic</span><span class="hspace"> </span><span class="RktVar">handler</span><span class="hspace"> </span><span class="RktMeta">...</span><span class="RktPn">)</span></p></blockquote></td></tr></table></td></tr><tr><td><table cellspacing="0" class="together"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>syntax</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(form._((lib._marketplace/sugar-untyped..rkt)._observe-publishers/everything))"></a><span class="RktSym"><a href="high-level-interface.html#%28form._%28%28lib._marketplace%2Fsugar-untyped..rkt%29._observe-publishers%2Feverything%29%29" class="RktStxDef RktStxLink" data-pltdoc="x">observe-publishers/everything</a></span><span class="hspace"> </span><span class="RktVar">topic</span><span class="hspace"> </span><span class="RktVar">handler</span><span class="hspace"> </span><span class="RktMeta">...</span><span class="RktPn">)</span></p></blockquote></td></tr></table></td></tr><tr><td><table cellspacing="0" class="together"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>syntax</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(form._((lib._marketplace/sugar-typed..rkt)._observe-publishers/everything~3a))"></a><span class="RktSym"><a href="high-level-interface.html#%28form._%28%28lib._marketplace%2Fsugar-typed..rkt%29._observe-publishers%2Feverything~3a%29%29" class="RktStxDef RktStxLink" data-pltdoc="x">observe-publishers/everything:</a></span><span class="hspace"> </span><span class="RktVar">State</span><span class="hspace"> </span><span class="RktVar">topic</span><span class="hspace"> </span><span class="RktVar">handler</span><span class="hspace"> </span><span class="RktMeta">...</span><span class="RktPn">)</span></p></blockquote></td></tr></table></td></tr><tr><td><table cellspacing="0" class="together"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>syntax</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(form._((lib._marketplace/sugar-untyped..rkt)._build-endpoint))"></a><span class="RktSym"><a href="high-level-interface.html#%28form._%28%28lib._marketplace%2Fsugar-untyped..rkt%29._build-endpoint%29%29" class="RktStxDef RktStxLink" data-pltdoc="x">build-endpoint</a></span><span class="hspace"> </span><span class="RktVar">pre-eid</span><span class="hspace"> </span><span class="RktVar">role</span><span class="hspace"> </span><span class="RktVar">handler</span><span class="hspace"> </span><span class="RktMeta">...</span><span class="RktPn">)</span></p></blockquote></td></tr></table></td></tr><tr><td><table cellspacing="0" class="together"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>syntax</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(form._((lib._marketplace/sugar-typed..rkt)._build-endpoint~3a))"></a><span class="RktSym"><a href="high-level-interface.html#%28form._%28%28lib._marketplace%2Fsugar-typed..rkt%29._build-endpoint~3a%29%29" class="RktStxDef RktStxLink" data-pltdoc="x">build-endpoint:</a></span><span class="hspace"> </span><span class="RktVar">State</span><span class="hspace"> </span><span class="RktVar">pre-eid</span><span class="hspace"> </span><span class="RktVar">role</span><span class="hspace"> </span><span class="RktVar">handler</span><span class="hspace"> </span><span class="RktMeta">...</span><span class="RktPn">)</span></p></blockquote></td></tr></table></td></tr></table></blockquote></div><div class="SIntrapara">The many variations on the core
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<span class="RktSym"><a href="high-level-interface.html#%28form._%28%28lib._marketplace%2Fsugar-untyped..rkt%29._build-endpoint%29%29" class="RktStxLink" data-pltdoc="x">build-endpoint</a></span>/<span class="RktSym"><a href="high-level-interface.html#%28form._%28%28lib._marketplace%2Fsugar-typed..rkt%29._build-endpoint~3a%29%29" class="RktStxLink" data-pltdoc="x">build-endpoint:</a></span> form exist to give
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good control over <span class="RktSym"><a href="low-level-interface.html#%28def._%28%28lib._marketplace%2Fmain..rkt%29._.Interest.Type%29%29" class="RktValLink" data-pltdoc="x">InterestType</a></span> in the endpoint under
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construction;
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see <a href="high-level-interface.html#%28part._participating-vs-observing%29" data-pltdoc="x">Participating in a conversation vs. observing conversations</a>.</div></p><p>Almost everything is optional in an endpoint definition. The only
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mandatory part is the topic, unless you’re using Typed Racket, in
|
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which case the process state type must also be specified.</p><p>For example, a minimal endpoint subscribing to all messages would be:</p><blockquote class="SCodeFlow"><p><span class="RktPn">(</span><span class="RktSym"><a href="high-level-interface.html#%28form._%28%28lib._marketplace%2Fsugar-untyped..rkt%29._subscriber%29%29" class="RktStxLink" data-pltdoc="x">subscriber</a></span><span class="hspace"> </span><span class="RktSym"><a href="low-level-interface.html#%28def._%28%28lib._marketplace%2Fsugar-untyped..rkt%29._~3f%29%29" class="RktValLink" data-pltdoc="x">?</a></span><span class="RktPn">)</span></p></blockquote><p>or in Typed Racket, for a process with <span class="RktSym"><a href="http://docs.racket-lang.org/ts-reference/type-ref.html#%28form._%28%28lib._typed-racket%2Fbase-env%2Fbase-types..rkt%29._.Integer%29%29" class="RktStxLink" data-pltdoc="x">Integer</a></span> as its process
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state type,</p><blockquote class="SCodeFlow"><p><span class="RktPn">(</span><span class="RktSym"><a href="high-level-interface.html#%28form._%28%28lib._marketplace%2Fsugar-typed..rkt%29._subscriber~3a%29%29" class="RktStxLink" data-pltdoc="x">subscriber:</a></span><span class="hspace"> </span><span class="RktSym"><a href="http://docs.racket-lang.org/ts-reference/type-ref.html#%28form._%28%28lib._typed-racket%2Fbase-env%2Fbase-types..rkt%29._.Integer%29%29" class="RktStxLink" data-pltdoc="x">Integer</a></span><span class="hspace"> </span><span class="RktSym"><a href="low-level-interface.html#%28def._%28%28lib._marketplace%2Fsugar-untyped..rkt%29._~3f%29%29" class="RktValLink" data-pltdoc="x">?</a></span><span class="RktPn">)</span></p></blockquote><p>A minimal publishing endpoint would be:</p><blockquote class="SCodeFlow"><table cellspacing="0" class="RktBlk"><tr><td><span class="RktPn">(</span><span class="RktSym"><a href="high-level-interface.html#%28form._%28%28lib._marketplace%2Fsugar-untyped..rkt%29._publisher%29%29" class="RktStxLink" data-pltdoc="x">publisher</a></span><span class="hspace"> </span><span class="RktSym"><a href="low-level-interface.html#%28def._%28%28lib._marketplace%2Fsugar-untyped..rkt%29._~3f%29%29" class="RktValLink" data-pltdoc="x">?</a></span><span class="RktPn">)</span></td></tr><tr><td><span class="RktPn">(</span><span class="RktSym"><a href="high-level-interface.html#%28form._%28%28lib._marketplace%2Fsugar-typed..rkt%29._publisher~3a%29%29" class="RktStxLink" data-pltdoc="x">publisher:</a></span><span class="hspace"> </span><span class="RktSym"><a href="http://docs.racket-lang.org/ts-reference/type-ref.html#%28form._%28%28lib._typed-racket%2Fbase-env%2Fbase-types..rkt%29._.Integer%29%29" class="RktStxLink" data-pltdoc="x">Integer</a></span><span class="hspace"> </span><span class="RktSym"><a href="low-level-interface.html#%28def._%28%28lib._marketplace%2Fsugar-untyped..rkt%29._~3f%29%29" class="RktValLink" data-pltdoc="x">?</a></span><span class="RktPn">)</span></td></tr></table></blockquote><p>While topic patterns are ordinary Racket data with embedded <span class="RktSym"><a href="low-level-interface.html#%28def._%28%28lib._marketplace%2Fsugar-untyped..rkt%29._~3f%29%29" class="RktValLink" data-pltdoc="x">?</a></span>
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wildcards (see <a href="Concepts.html#%28part._messages-and-topics%29" data-pltdoc="x">Messages and Topics</a>), all the other patterns
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in an endpoint definition are <span class="RktSym">match</span>-patterns. In particular
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note that <span class="RktSym"><a href="low-level-interface.html#%28def._%28%28lib._marketplace%2Fsugar-untyped..rkt%29._~3f%29%29" class="RktValLink" data-pltdoc="x">?</a></span> is a wildcard in a topic pattern, while
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<span class="RktSym"><a href="http://docs.racket-lang.org/reference/stx-patterns.html#%28form._%28%28lib._racket%2Fprivate%2Fstxcase-scheme..rkt%29.__%29%29" class="RktStxLink" data-pltdoc="x">_</a></span> is a wildcard in a <span class="RktSym">match</span>-pattern.</p><h5>2.4.1<tt> </tt><a name="(part._.Receiving_messages)"></a>Receiving messages</h5><p><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>syntax</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(form._((lib._marketplace/sugar-untyped..rkt)._on-message))"></a><span class="RktSym"><a href="high-level-interface.html#%28form._%28%28lib._marketplace%2Fsugar-untyped..rkt%29._on-message%29%29" class="RktStxDef RktStxLink" data-pltdoc="x">on-message</a></span><span class="hspace"> </span><span class="RktPn">[</span><span class="RktVar">pattern</span><span class="hspace"> </span><span class="RktVar">expr</span><span class="hspace"> </span><span class="RktMeta">...</span><span class="RktPn">]</span><span class="hspace"> </span><span class="RktMeta">...</span><span class="RktPn">)</span></p></blockquote></td></tr></table></blockquote></div><div class="SIntrapara">Supply an <span class="RktSym"><a href="high-level-interface.html#%28form._%28%28lib._marketplace%2Fsugar-untyped..rkt%29._on-message%29%29" class="RktStxLink" data-pltdoc="x">on-message</a></span> handler clause to an endpoint definition
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to handle incoming message events (as distinct from presence- or
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absence-events).</div></p><p>The following endpoint <span style="font-style: italic">subscribes</span> to all messages, but only
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<span style="font-style: italic">handles</span> some of them:</p><blockquote class="SCodeFlow"><table cellspacing="0" class="RktBlk"><tr><td><span class="RktPn">(</span><span class="RktSym"><a href="high-level-interface.html#%28form._%28%28lib._marketplace%2Fsugar-untyped..rkt%29._subscriber%29%29" class="RktStxLink" data-pltdoc="x">subscriber</a></span><span class="hspace"> </span><span class="RktSym"><a href="low-level-interface.html#%28def._%28%28lib._marketplace%2Fsugar-untyped..rkt%29._~3f%29%29" class="RktValLink" data-pltdoc="x">?</a></span></td></tr><tr><td><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="high-level-interface.html#%28form._%28%28lib._marketplace%2Fsugar-untyped..rkt%29._on-message%29%29" class="RktStxLink" data-pltdoc="x">on-message</a></span></td></tr><tr><td><span class="hspace"> </span><span class="RktPn">[</span><span class="RktVal">'</span><span class="RktVal">ping</span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="high-level-interface.html#%28def._%28%28lib._marketplace%2Fsugar-values..rkt%29._send-message%29%29" class="RktValLink" data-pltdoc="x">send-message</a></span><span class="hspace"> </span><span class="RktVal">'</span><span class="RktVal">pong</span><span class="RktPn">)</span><span class="RktPn">]</span></td></tr><tr><td><span class="hspace"> </span><span class="RktPn">[</span><span class="RktVal">'</span><span class="RktVal">hello</span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="http://docs.racket-lang.org/reference/pairs.html#%28def._%28%28quote._~23~25kernel%29._list%29%29" class="RktValLink" data-pltdoc="x">list</a></span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="high-level-interface.html#%28def._%28%28lib._marketplace%2Fsugar-values..rkt%29._send-message%29%29" class="RktValLink" data-pltdoc="x">send-message</a></span><span class="hspace"> </span><span class="RktVal">'</span><span class="RktVal">goodbye</span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="high-level-interface.html#%28def._%28%28lib._marketplace%2Fsugar-values..rkt%29._quit%29%29" class="RktValLink" data-pltdoc="x">quit</a></span><span class="RktPn">)</span><span class="RktPn">)</span><span class="RktPn">]</span><span class="RktPn">)</span><span class="RktPn">)</span></td></tr></table></blockquote><h5>2.4.2<tt> </tt><a name="(part._.Action-only_vs__.State_updates)"></a>Action-only vs. State updates</h5><p><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>syntax</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(form._((lib._marketplace/sugar-untyped..rkt)._match-state))"></a><span class="RktSym"><a href="high-level-interface.html#%28form._%28%28lib._marketplace%2Fsugar-untyped..rkt%29._match-state%29%29" class="RktStxDef RktStxLink" data-pltdoc="x">match-state</a></span><span class="hspace"> </span><span class="RktVar">pattern</span><span class="hspace"> </span><span class="RktVar">handler</span><span class="hspace"> </span><span class="RktMeta">...</span><span class="RktPn">)</span></p></blockquote></td></tr></table></blockquote></div><div class="SIntrapara">If a group of handlers is wrapped in <span class="RktSym"><a href="high-level-interface.html#%28form._%28%28lib._marketplace%2Fsugar-untyped..rkt%29._match-state%29%29" class="RktStxLink" data-pltdoc="x">match-state</a></span>, then all
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the wrapped handlers are expected to return
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<a href="high-level-interface.html#%28part._constructing-transitions%29" data-pltdoc="x">transition structures</a>.</div></p><p>If not, however, the handler expressions are expected to return plain
|
|
<span class="RktSym"><a href="high-level-interface.html#%28def._%28%28lib._marketplace%2Fmain..rkt%29._.Action.Tree%29%29" class="RktValLink" data-pltdoc="x">ActionTree</a></span>s.</p><p>This way, simple handlers that do not need to examine the process
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state, and simply act in response to whichever event triggered them,
|
|
can be written without the clutter of threading the process state
|
|
value through the code.</p><p>For example, a simple endpoint could be written either as</p><blockquote class="SCodeFlow"><table cellspacing="0" class="RktBlk"><tr><td><span class="RktPn">(</span><span class="RktSym"><a href="high-level-interface.html#%28form._%28%28lib._marketplace%2Fsugar-untyped..rkt%29._subscriber%29%29" class="RktStxLink" data-pltdoc="x">subscriber</a></span><span class="hspace"> </span><span class="RktVal">'</span><span class="RktVal">ping</span></td></tr><tr><td><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="high-level-interface.html#%28form._%28%28lib._marketplace%2Fsugar-untyped..rkt%29._on-message%29%29" class="RktStxLink" data-pltdoc="x">on-message</a></span><span class="hspace"> </span><span class="RktPn">[</span><span class="RktVal">'</span><span class="RktVal">ping</span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="high-level-interface.html#%28def._%28%28lib._marketplace%2Fsugar-values..rkt%29._send-message%29%29" class="RktValLink" data-pltdoc="x">send-message</a></span><span class="hspace"> </span><span class="RktVal">'</span><span class="RktVal">pong</span><span class="RktPn">)</span><span class="RktPn">]</span><span class="RktPn">)</span><span class="RktPn">)</span></td></tr></table></blockquote><p>or, explicitly accessing the endpoint’s process’s state,</p><blockquote class="SCodeFlow"><table cellspacing="0" class="RktBlk"><tr><td><span class="RktPn">(</span><span class="RktSym"><a href="high-level-interface.html#%28form._%28%28lib._marketplace%2Fsugar-untyped..rkt%29._subscriber%29%29" class="RktStxLink" data-pltdoc="x">subscriber</a></span><span class="hspace"> </span><span class="RktVal">'</span><span class="RktVal">ping</span></td></tr><tr><td><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="high-level-interface.html#%28form._%28%28lib._marketplace%2Fsugar-untyped..rkt%29._match-state%29%29" class="RktStxLink" data-pltdoc="x">match-state</a></span><span class="hspace"> </span><span class="RktSym">old-state</span></td></tr><tr><td><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="high-level-interface.html#%28form._%28%28lib._marketplace%2Fsugar-untyped..rkt%29._on-message%29%29" class="RktStxLink" data-pltdoc="x">on-message</a></span><span class="hspace"> </span><span class="RktPn">[</span><span class="RktVal">'</span><span class="RktVal">ping</span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="high-level-interface.html#%28form._%28%28lib._marketplace%2Fsugar-values..rkt%29._transition%29%29" class="RktStxLink" data-pltdoc="x">transition</a></span><span class="hspace"> </span><span class="RktSym">old-state</span></td></tr><tr><td><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="high-level-interface.html#%28def._%28%28lib._marketplace%2Fsugar-values..rkt%29._send-message%29%29" class="RktValLink" data-pltdoc="x">send-message</a></span><span class="hspace"> </span><span class="RktVal">'</span><span class="RktVal">pong</span><span class="RktPn">)</span><span class="RktPn">)</span><span class="RktPn">]</span><span class="RktPn">)</span><span class="RktPn">)</span><span class="RktPn">)</span></td></tr></table></blockquote><h5>2.4.3<tt> </tt><a name="(part._.Handling_presence_and_absence_events)"></a>Handling presence and absence events</h5><p><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" class="boxed RBoxed"><tr><td><table cellspacing="0" class="together"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>syntax</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(form._((lib._marketplace/sugar-untyped..rkt)._on-presence))"></a><span class="RktSym"><a href="high-level-interface.html#%28form._%28%28lib._marketplace%2Fsugar-untyped..rkt%29._on-presence%29%29" class="RktStxDef RktStxLink" data-pltdoc="x">on-presence</a></span><span class="hspace"> </span><span class="RktVar">expr</span><span class="hspace"> </span><span class="RktMeta">...</span><span class="RktPn">)</span></p></blockquote></td></tr></table></td></tr><tr><td><table cellspacing="0" class="together"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>syntax</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(form._((lib._marketplace/sugar-untyped..rkt)._on-absence))"></a><span class="RktSym"><a href="high-level-interface.html#%28form._%28%28lib._marketplace%2Fsugar-untyped..rkt%29._on-absence%29%29" class="RktStxDef RktStxLink" data-pltdoc="x">on-absence</a></span><span class="hspace"> </span><span class="RktVar">expr</span><span class="hspace"> </span><span class="RktMeta">...</span><span class="RktPn">)</span></p></blockquote></td></tr></table></td></tr></table></blockquote></div><div class="SIntrapara">Other endpoints (in this or other processes) may have matching topics
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and complementary orientations to the current endpoint. When such
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endpoints come and go, presence and absence events are generated in
|
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the current endpoint.</div></p><p>By default, no actions are taken on such events, but
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<span class="RktSym"><a href="high-level-interface.html#%28form._%28%28lib._marketplace%2Fsugar-untyped..rkt%29._on-presence%29%29" class="RktStxLink" data-pltdoc="x">on-presence</a></span> and <span class="RktSym"><a href="high-level-interface.html#%28form._%28%28lib._marketplace%2Fsugar-untyped..rkt%29._on-absence%29%29" class="RktStxLink" data-pltdoc="x">on-absence</a></span> handlers override this
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behaviour.</p><p>For example, say process A establishes the following endpoint:</p><blockquote class="SCodeFlow"><table cellspacing="0" class="RktBlk"><tr><td><span class="RktPn">(</span><span class="RktSym"><a href="high-level-interface.html#%28form._%28%28lib._marketplace%2Fsugar-untyped..rkt%29._subscriber%29%29" class="RktStxLink" data-pltdoc="x">subscriber</a></span><span class="hspace"> </span><span class="RktVal">'</span><span class="RktVal">ping</span></td></tr><tr><td><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="high-level-interface.html#%28form._%28%28lib._marketplace%2Fsugar-untyped..rkt%29._on-presence%29%29" class="RktStxLink" data-pltdoc="x">on-presence</a></span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="high-level-interface.html#%28def._%28%28lib._marketplace%2Fsugar-values..rkt%29._send-message%29%29" class="RktValLink" data-pltdoc="x">send-message</a></span><span class="hspace"> </span><span class="RktVal">'</span><span class="RktVal">pinger-arrived</span><span class="RktPn">)</span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="high-level-interface.html#%28form._%28%28lib._marketplace%2Fsugar-untyped..rkt%29._on-absence%29%29" class="RktStxLink" data-pltdoc="x">on-absence</a></span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="high-level-interface.html#%28def._%28%28lib._marketplace%2Fsugar-values..rkt%29._send-message%29%29" class="RktValLink" data-pltdoc="x">send-message</a></span><span class="hspace"> </span><span class="RktVal">'</span><span class="RktVal">pinger-departed</span><span class="RktPn">)</span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="high-level-interface.html#%28form._%28%28lib._marketplace%2Fsugar-untyped..rkt%29._on-message%29%29" class="RktStxLink" data-pltdoc="x">on-message</a></span><span class="hspace"> </span><span class="RktPn">[</span><span class="RktVal">'</span><span class="RktVal">ping</span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="high-level-interface.html#%28def._%28%28lib._marketplace%2Fsugar-values..rkt%29._send-message%29%29" class="RktValLink" data-pltdoc="x">send-message</a></span><span class="hspace"> </span><span class="RktVal">'</span><span class="RktVal">pong</span><span class="RktPn">)</span><span class="RktPn">]</span><span class="RktPn">)</span><span class="RktPn">)</span></td></tr></table></blockquote><p>Some time later, process B takes the following endpoint-establishing
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action:</p><blockquote class="SCodeFlow"><table cellspacing="0" class="RktBlk"><tr><td><span class="RktPn">(</span><span class="RktSym"><a href="high-level-interface.html#%28form._%28%28lib._marketplace%2Fsugar-untyped..rkt%29._let-fresh%29%29" class="RktStxLink" data-pltdoc="x">let-fresh</a></span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym">ping-endpoint-name</span><span class="hspace"> </span><span class="RktSym">pong-waiter-name</span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="high-level-interface.html#%28def._%28%28lib._marketplace%2Fsugar-typed..rkt%29._name-endpoint%29%29" class="RktValLink" data-pltdoc="x">name-endpoint</a></span><span class="hspace"> </span><span class="RktSym">ping-endpoint-name</span></td></tr><tr><td><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="high-level-interface.html#%28form._%28%28lib._marketplace%2Fsugar-untyped..rkt%29._publisher%29%29" class="RktStxLink" data-pltdoc="x">publisher</a></span><span class="hspace"> </span><span class="RktVal">'</span><span class="RktVal">ping</span></td></tr><tr><td><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="high-level-interface.html#%28form._%28%28lib._marketplace%2Fsugar-untyped..rkt%29._on-presence%29%29" class="RktStxLink" data-pltdoc="x">on-presence</a></span></td></tr><tr><td><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="http://docs.racket-lang.org/reference/pairs.html#%28def._%28%28quote._~23~25kernel%29._list%29%29" class="RktValLink" data-pltdoc="x">list</a></span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="high-level-interface.html#%28def._%28%28lib._marketplace%2Fsugar-typed..rkt%29._name-endpoint%29%29" class="RktValLink" data-pltdoc="x">name-endpoint</a></span><span class="hspace"> </span><span class="RktSym">pong-waiter-name</span></td></tr><tr><td><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="high-level-interface.html#%28form._%28%28lib._marketplace%2Fsugar-untyped..rkt%29._subscriber%29%29" class="RktStxLink" data-pltdoc="x">subscriber</a></span><span class="hspace"> </span><span class="RktVal">'</span><span class="RktVal">pong</span></td></tr><tr><td><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="high-level-interface.html#%28form._%28%28lib._marketplace%2Fsugar-untyped..rkt%29._on-message%29%29" class="RktStxLink" data-pltdoc="x">on-message</a></span></td></tr><tr><td><span class="hspace"> </span><span class="RktPn">[</span><span class="RktVal">'</span><span class="RktVal">pong</span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="http://docs.racket-lang.org/reference/pairs.html#%28def._%28%28quote._~23~25kernel%29._list%29%29" class="RktValLink" data-pltdoc="x">list</a></span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="high-level-interface.html#%28def._%28%28lib._marketplace%2Fsugar-values..rkt%29._delete-endpoint%29%29" class="RktValLink" data-pltdoc="x">delete-endpoint</a></span><span class="hspace"> </span><span class="RktSym">ping-endpoint-name</span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="high-level-interface.html#%28def._%28%28lib._marketplace%2Fsugar-values..rkt%29._delete-endpoint%29%29" class="RktValLink" data-pltdoc="x">delete-endpoint</a></span><span class="hspace"> </span><span class="RktSym">pong-waiter-name</span><span class="RktPn">)</span><span class="RktPn">)</span><span class="RktPn">]</span><span class="RktPn">)</span><span class="RktPn">)</span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="high-level-interface.html#%28def._%28%28lib._marketplace%2Fsugar-values..rkt%29._send-message%29%29" class="RktValLink" data-pltdoc="x">send-message</a></span><span class="hspace"> </span><span class="RktVal">'</span><span class="RktVal">ping</span><span class="RktPn">)</span><span class="RktPn">)</span><span class="RktPn">)</span><span class="RktPn">)</span><span class="RktPn">)</span><span class="RktPn">)</span></td></tr></table></blockquote><p>The sequence of events will be:</p><ol><li><p>Process A’s <span class="RktSym"><a href="high-level-interface.html#%28form._%28%28lib._marketplace%2Fsugar-untyped..rkt%29._on-presence%29%29" class="RktStxLink" data-pltdoc="x">on-presence</a></span> handler will run, and the
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<span class="RktVal">'</span><span class="RktVal">pinger-arrived</span> message will be sent. At the same
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time,<span class="NoteBox"><span class="NoteContent">In the current implementation, one happens before the
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other, but it is nondeterministic which is run first.</span></span> process B’s
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<span class="RktSym"><a href="high-level-interface.html#%28form._%28%28lib._marketplace%2Fsugar-untyped..rkt%29._on-presence%29%29" class="RktStxLink" data-pltdoc="x">on-presence</a></span> handler runs, installing a second endpoint
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and sending the <span class="RktVal">'</span><span class="RktVal">ping</span> message.</p></li><li><p>Process A’s endpoint receives the <span class="RktVal">'</span><span class="RktVal">ping</span> message, and
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sends the <span class="RktVal">'</span><span class="RktVal">pong</span> message.</p></li><li><p>Process B’s second endpoint receives the <span class="RktVal">'</span><span class="RktVal">pong</span>
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message, and deletes both of process B’s endpoints.</p></li><li><p>The <span class="RktSym"><a href="high-level-interface.html#%28form._%28%28lib._marketplace%2Fsugar-untyped..rkt%29._on-absence%29%29" class="RktStxLink" data-pltdoc="x">on-absence</a></span> handler in process A runs, sending
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the <span class="RktVal">'</span><span class="RktVal">pinger-departed</span> message.</p></li></ol><p>One possible trace of messages in the VM containing processes A and B is</p><blockquote class="SCodeFlow"><table cellspacing="0" class="RktBlk"><tr><td><span class="RktVal">'</span><span class="RktVal">pinger-arrived</span></td></tr><tr><td><span class="RktVal">'</span><span class="RktVal">ping</span></td></tr><tr><td><span class="RktVal">'</span><span class="RktVal">pong</span></td></tr><tr><td><span class="RktVal">'</span><span class="RktVal">pinger-departed</span></td></tr></table></blockquote><p>By sending the <span class="RktVal">'</span><span class="RktVal">ping</span> message <span style="font-style: italic">only</span> once the
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<span class="RktSym"><a href="high-level-interface.html#%28form._%28%28lib._marketplace%2Fsugar-untyped..rkt%29._on-presence%29%29" class="RktStxLink" data-pltdoc="x">on-presence</a></span> handler has fired, process B ensures that
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someone is listening for pings.</p><p>This way, if process B starts before process A, then B will
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|
automatically wait until A is ready to receive ping requests before
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issuing any.</p><h5>2.4.4<tt> </tt><a name="(part._.Exit_reasons)"></a>Exit reasons</h5><p><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>syntax</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(form._((lib._marketplace/sugar-untyped..rkt)._match-reason))"></a><span class="RktSym"><a href="high-level-interface.html#%28form._%28%28lib._marketplace%2Fsugar-untyped..rkt%29._match-reason%29%29" class="RktStxDef RktStxLink" data-pltdoc="x">match-reason</a></span><span class="hspace"> </span><span class="RktVar">pattern</span><span class="hspace"> </span><span class="RktVar">handler</span><span class="hspace"> </span><span class="RktMeta">...</span><span class="RktPn">)</span></p></blockquote></td></tr></table></blockquote></div><div class="SIntrapara">If a handler is wrapped in a <span class="RktSym"><a href="high-level-interface.html#%28form._%28%28lib._marketplace%2Fsugar-untyped..rkt%29._match-reason%29%29" class="RktStxLink" data-pltdoc="x">match-reason</a></span> form, then the exit
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reason supplied to the <span class="RktSym"><a href="high-level-interface.html#%28def._%28%28lib._marketplace%2Fsugar-values..rkt%29._delete-endpoint%29%29" class="RktValLink" data-pltdoc="x">delete-endpoint</a></span> or <span class="RktSym"><a href="high-level-interface.html#%28def._%28%28lib._marketplace%2Fsugar-values..rkt%29._quit%29%29" class="RktValLink" data-pltdoc="x">quit</a></span>
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|
action that led to the <span class="RktSym"><a href="low-level-interface.html#%28def._%28%28lib._marketplace%2Fmain..rkt%29._absence-event%29%29" class="RktValLink" data-pltdoc="x">absence-event</a></span> is available to the
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endpoint’s <span class="RktSym"><a href="high-level-interface.html#%28form._%28%28lib._marketplace%2Fsugar-untyped..rkt%29._on-absence%29%29" class="RktStxLink" data-pltdoc="x">on-absence</a></span> handler expression.</div></p><h5>2.4.5<tt> </tt><a name="(part._updating-endpoints)"></a>Updating endpoints</h5><p>If, when an endpoint is created, an existing endpoint with an
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<span class="RktSym"><a href="http://docs.racket-lang.org/reference/booleans.html#%28def._%28%28quote._~23~25kernel%29._equal~3f%29%29" class="RktValLink" data-pltdoc="x">equal?</a></span> name is already present, then if the existing and
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to-be-added endpoints have exactly equal roles (meaning equal
|
|
orientations, interest-types, and topic patterns), the <span style="font-style: italic">handlers</span>
|
|
for the endpoint are <span style="font-style: italic">updated</span> without emitting presence or
|
|
absence notifications.</p><p>This dubious feature can be used to avoid "glitching" of presence
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signals. A future release of this library will include better
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|
automatic support for avoiding such transients.</p><h5>2.4.6<tt> </tt><a name="(part._.Who_am_.I_talking_to_)"></a>Who am I talking to?</h5><p><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" class="boxed RBoxed"><tr><td><table cellspacing="0" class="together"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>syntax</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(form._((lib._marketplace/sugar-untyped..rkt)._match-orientation))"></a><span class="RktSym"><a href="high-level-interface.html#%28form._%28%28lib._marketplace%2Fsugar-untyped..rkt%29._match-orientation%29%29" class="RktStxDef RktStxLink" data-pltdoc="x">match-orientation</a></span><span class="hspace"> </span><span class="RktVar">pattern</span><span class="hspace"> </span><span class="RktVar">handler</span><span class="hspace"> </span><span class="RktMeta">...</span><span class="RktPn">)</span></p></blockquote></td></tr></table></td></tr><tr><td><table cellspacing="0" class="together"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>syntax</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(form._((lib._marketplace/sugar-untyped..rkt)._match-conversation))"></a><span class="RktSym"><a href="high-level-interface.html#%28form._%28%28lib._marketplace%2Fsugar-untyped..rkt%29._match-conversation%29%29" class="RktStxDef RktStxLink" data-pltdoc="x">match-conversation</a></span><span class="hspace"> </span><span class="RktVar">pattern</span><span class="hspace"> </span><span class="RktVar">handler</span><span class="hspace"> </span><span class="RktMeta">...</span><span class="RktPn">)</span></p></blockquote></td></tr></table></td></tr><tr><td><table cellspacing="0" class="together"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>syntax</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(form._((lib._marketplace/sugar-untyped..rkt)._match-interest-type))"></a><span class="RktSym"><a href="high-level-interface.html#%28form._%28%28lib._marketplace%2Fsugar-untyped..rkt%29._match-interest-type%29%29" class="RktStxDef RktStxLink" data-pltdoc="x">match-interest-type</a></span><span class="hspace"> </span><span class="RktVar">pattern</span><span class="hspace"> </span><span class="RktVar">handler</span><span class="hspace"> </span><span class="RktMeta">...</span><span class="RktPn">)</span></p></blockquote></td></tr></table></td></tr></table></blockquote></div><div class="SIntrapara">Wrapping a handler in <span class="RktSym"><a href="high-level-interface.html#%28form._%28%28lib._marketplace%2Fsugar-untyped..rkt%29._match-orientation%29%29" class="RktStxLink" data-pltdoc="x">match-orientation</a></span>,
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<span class="RktSym"><a href="high-level-interface.html#%28form._%28%28lib._marketplace%2Fsugar-untyped..rkt%29._match-conversation%29%29" class="RktStxLink" data-pltdoc="x">match-conversation</a></span>, and/or <span class="RktSym"><a href="high-level-interface.html#%28form._%28%28lib._marketplace%2Fsugar-untyped..rkt%29._match-interest-type%29%29" class="RktStxLink" data-pltdoc="x">match-interest-type</a></span> gives
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|
a handler access to the contents of the <span class="RktSym"><a href="low-level-interface.html#%28def._%28%28lib._marketplace%2Fmain..rkt%29._role%29%29" class="RktValLink" data-pltdoc="x">role</a></span> structure
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carried in the triggering <span class="RktSym"><a href="low-level-interface.html#%28def._%28%28lib._marketplace%2Fmain..rkt%29._.Endpoint.Event%29%29" class="RktValLink" data-pltdoc="x">EndpointEvent</a></span>.</div></p><p>The carried role describes the <span style="font-style: italic">intersection of interests</span>
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|
between the current endpoint and the peer endpoint, and so can proxy
|
|
for the identity of the other party. It is in a sense a description of
|
|
the scope of the current conversation.</p><p>It is most common to simply use <span class="RktSym"><a href="high-level-interface.html#%28form._%28%28lib._marketplace%2Fsugar-untyped..rkt%29._match-conversation%29%29" class="RktStxLink" data-pltdoc="x">match-conversation</a></span> to extract
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|
the <span class="RktSym"><a href="low-level-interface.html#%28def._%28%28lib._marketplace%2Fmain..rkt%29._role-topic%29%29" class="RktValLink" data-pltdoc="x">role-topic</a></span> alone, since it is seldom necessary to examine
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|
<span class="RktSym"><a href="low-level-interface.html#%28def._%28%28lib._marketplace%2Fmain..rkt%29._role-orientation%29%29" class="RktValLink" data-pltdoc="x">role-orientation</a></span> (since it’s guaranteed to be complementary
|
|
to the orientation of the current endpoint) or
|
|
<span class="RktSym"><a href="low-level-interface.html#%28def._%28%28lib._marketplace%2Fmain..rkt%29._role-interest-type%29%29" class="RktValLink" data-pltdoc="x">role-interest-type</a></span>.</p><p>See <a href="Examples.html" data-pltdoc="x">Examples</a> for examples of the use of
|
|
<span class="RktSym"><a href="high-level-interface.html#%28form._%28%28lib._marketplace%2Fsugar-untyped..rkt%29._match-conversation%29%29" class="RktStxLink" data-pltdoc="x">match-conversation</a></span> and friends.</p><h5>2.4.7<tt> </tt><a name="(part._participating-vs-observing)"></a>Participating in a conversation vs. observing conversations</h5><p>The core <span class="RktSym"><a href="high-level-interface.html#%28form._%28%28lib._marketplace%2Fsugar-untyped..rkt%29._build-endpoint%29%29" class="RktStxLink" data-pltdoc="x">build-endpoint</a></span> form takes an expression evaluating
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to a <span class="RktSym"><a href="low-level-interface.html#%28def._%28%28lib._marketplace%2Fmain..rkt%29._role%29%29" class="RktValLink" data-pltdoc="x">role</a></span>, rather than a simple topic. This gives full
|
|
control over the new endpoint’s <span class="RktSym"><a href="low-level-interface.html#%28def._%28%28lib._marketplace%2Fmain..rkt%29._.Orientation%29%29" class="RktValLink" data-pltdoc="x">Orientation</a></span> and
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<span class="RktSym"><a href="low-level-interface.html#%28def._%28%28lib._marketplace%2Fmain..rkt%29._.Interest.Type%29%29" class="RktValLink" data-pltdoc="x">InterestType</a></span>.</p><p>The other forms exist for convenience, since usually the orientation
|
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and interest-type is known statically, and only the topic varies
|
|
dynamically:</p><ul><li><p><span class="RktSym"><a href="high-level-interface.html#%28form._%28%28lib._marketplace%2Fsugar-untyped..rkt%29._publisher%29%29" class="RktStxLink" data-pltdoc="x">publisher</a></span> and <span class="RktSym"><a href="high-level-interface.html#%28form._%28%28lib._marketplace%2Fsugar-untyped..rkt%29._subscriber%29%29" class="RktStxLink" data-pltdoc="x">subscriber</a></span> (and typed
|
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variations ending in <span class="stt">:</span>) are for ordinary <span style="font-style: italic">participation</span> in
|
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conversations;</p></li><li><p><span class="RktSym"><a href="high-level-interface.html#%28form._%28%28lib._marketplace%2Fsugar-untyped..rkt%29._observe-subscribers%29%29" class="RktStxLink" data-pltdoc="x">observe-subscribers</a></span> and <span class="RktSym"><a href="high-level-interface.html#%28form._%28%28lib._marketplace%2Fsugar-untyped..rkt%29._observe-publishers%29%29" class="RktStxLink" data-pltdoc="x">observe-publishers</a></span>
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are for <span style="font-style: italic">observing</span> conversations without participating in them; and</p></li><li><p><span class="RktSym"><a href="high-level-interface.html#%28form._%28%28lib._marketplace%2Fsugar-untyped..rkt%29._observe-subscribers%2Feverything%29%29" class="RktStxLink" data-pltdoc="x">observe-subscribers/everything</a></span> and
|
|
<span class="RktSym"><a href="high-level-interface.html#%28form._%28%28lib._marketplace%2Fsugar-untyped..rkt%29._observe-publishers%2Feverything%29%29" class="RktStxLink" data-pltdoc="x">observe-publishers/everything</a></span> are like the ordinary
|
|
<span class="stt">observe-...</span> variants, but use interest-type <span class="RktVal">'</span><span class="RktVal">everything</span>
|
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instead of <span class="RktVal">'</span><span class="RktVal">observer</span>.</p></li></ul><p>The <span class="RktSym"><a href="high-level-interface.html#%28form._%28%28lib._marketplace%2Fsugar-untyped..rkt%29._publisher%29%29" class="RktStxLink" data-pltdoc="x">publisher</a></span>, <span class="RktSym"><a href="high-level-interface.html#%28form._%28%28lib._marketplace%2Fsugar-untyped..rkt%29._observe-subscribers%29%29" class="RktStxLink" data-pltdoc="x">observe-subscribers</a></span> and
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<span class="RktSym"><a href="high-level-interface.html#%28form._%28%28lib._marketplace%2Fsugar-untyped..rkt%29._observe-subscribers%2Feverything%29%29" class="RktStxLink" data-pltdoc="x">observe-subscribers/everything</a></span> forms create
|
|
<span style="font-style: italic">publisher</span>-oriented endpoints, and <span class="RktSym"><a href="high-level-interface.html#%28form._%28%28lib._marketplace%2Fsugar-untyped..rkt%29._subscriber%29%29" class="RktStxLink" data-pltdoc="x">subscriber</a></span>,
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<span class="RktSym"><a href="high-level-interface.html#%28form._%28%28lib._marketplace%2Fsugar-untyped..rkt%29._observe-publishers%29%29" class="RktStxLink" data-pltdoc="x">observe-publishers</a></span> and <span class="RktSym"><a href="high-level-interface.html#%28form._%28%28lib._marketplace%2Fsugar-untyped..rkt%29._observe-publishers%2Feverything%29%29" class="RktStxLink" data-pltdoc="x">observe-publishers/everything</a></span>
|
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create <span style="font-style: italic">subscriber</span>-oriented endpoints. The rationale for this is
|
|
that as a participant, the code should declare the role being played;
|
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but as an observer, the code should declare the roles being observed.</p><h5>2.4.8<tt> </tt><a name="(part._naming-endpoints)"></a>Naming endpoints</h5><p>Endpoint names can be used to <a href="high-level-interface.html#%28part._updating-endpoints%29" data-pltdoc="x">update</a>
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or <a href="high-level-interface.html#%28part._deleting-endpoints%29" data-pltdoc="x">delete</a> endpoints.</p><p><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>procedure</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(def._((lib._marketplace/sugar-typed..rkt)._name-endpoint))"></a><span class="RktSym"><a href="high-level-interface.html#%28def._%28%28lib._marketplace%2Fsugar-typed..rkt%29._name-endpoint%29%29" class="RktValDef RktValLink" data-pltdoc="x">name-endpoint</a></span><span class="hspace"> </span><span class="RktVar">id</span><span class="hspace"> </span><span class="RktVar">add-endpoint-action</span><span class="RktPn">)</span><span class="hspace"> </span>→<span class="hspace"> </span><span class="RktSym"><a href="low-level-interface.html#%28def._%28%28lib._marketplace%2Fmain..rkt%29._.Add.Endpoint%29%29" class="RktValLink" data-pltdoc="x">AddEndpoint</a></span></p></blockquote></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">id</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym"><a href="http://docs.racket-lang.org/ts-reference/type-ref.html#%28form._%28%28lib._typed-racket%2Fbase-env%2Fbase-types..rkt%29._.Any%29%29" class="RktStxLink" data-pltdoc="x">Any</a></span></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">add-endpoint-action</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym"><a href="low-level-interface.html#%28def._%28%28lib._marketplace%2Fmain..rkt%29._.Add.Endpoint%29%29" class="RktValLink" data-pltdoc="x">AddEndpoint</a></span></td></tr></table></blockquote></div><div class="SIntrapara">Returns a copy of the passed-in <span class="RktSym"><a href="low-level-interface.html#%28def._%28%28lib._marketplace%2Fmain..rkt%29._add-endpoint%29%29" class="RktValLink" data-pltdoc="x">add-endpoint</a></span> action
|
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structure, with the <span class="RktVar">id</span> field set to the passed-in identifying
|
|
value.</div></p><p><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>syntax</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(form._((lib._marketplace/sugar-untyped..rkt)._let-fresh))"></a><span class="RktSym"><a href="high-level-interface.html#%28form._%28%28lib._marketplace%2Fsugar-untyped..rkt%29._let-fresh%29%29" class="RktStxDef RktStxLink" data-pltdoc="x">let-fresh</a></span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktVar">identifier</span><span class="hspace"> </span><span class="RktMeta">...</span><span class="RktPn">)</span><span class="hspace"> </span><span class="RktVar">expr</span><span class="hspace"> </span><span class="RktMeta">...</span><span class="RktPn">)</span></p></blockquote></td></tr></table></blockquote></div><div class="SIntrapara">Binds the <span class="RktVar">identifier</span>s to freshly-gensymmed symbols so that
|
|
they are available to the <span class="RktSym">exprs</span>. <span class="RktSym"><a href="high-level-interface.html#%28form._%28%28lib._marketplace%2Fsugar-untyped..rkt%29._let-fresh%29%29" class="RktStxLink" data-pltdoc="x">let-fresh</a></span> is useful
|
|
for inventing a guaranteed-unused name for a temporary endpoint:</div></p><blockquote class="SCodeFlow"><table cellspacing="0" class="RktBlk"><tr><td><span class="RktPn">(</span><span class="RktSym"><a href="high-level-interface.html#%28form._%28%28lib._marketplace%2Fsugar-untyped..rkt%29._let-fresh%29%29" class="RktStxLink" data-pltdoc="x">let-fresh</a></span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym">my-name</span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="high-level-interface.html#%28def._%28%28lib._marketplace%2Fsugar-typed..rkt%29._name-endpoint%29%29" class="RktValLink" data-pltdoc="x">name-endpoint</a></span><span class="hspace"> </span><span class="RktSym">my-name</span></td></tr><tr><td><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="high-level-interface.html#%28form._%28%28lib._marketplace%2Fsugar-untyped..rkt%29._subscriber%29%29" class="RktStxLink" data-pltdoc="x">subscriber</a></span><span class="hspace"> </span><span class="RktSym"><a href="low-level-interface.html#%28def._%28%28lib._marketplace%2Fsugar-untyped..rkt%29._~3f%29%29" class="RktValLink" data-pltdoc="x">?</a></span></td></tr><tr><td><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="high-level-interface.html#%28form._%28%28lib._marketplace%2Fsugar-untyped..rkt%29._on-message%29%29" class="RktStxLink" data-pltdoc="x">on-message</a></span><span class="hspace"> </span><span class="RktPn">[</span><span class="RktSym"><a href="http://docs.racket-lang.org/reference/stx-patterns.html#%28form._%28%28lib._racket%2Fprivate%2Fstxcase-scheme..rkt%29.__%29%29" class="RktStxLink" data-pltdoc="x">_</a></span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="http://docs.racket-lang.org/reference/pairs.html#%28def._%28%28quote._~23~25kernel%29._list%29%29" class="RktValLink" data-pltdoc="x">list</a></span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="high-level-interface.html#%28def._%28%28lib._marketplace%2Fsugar-values..rkt%29._delete-endpoint%29%29" class="RktValLink" data-pltdoc="x">delete-endpoint</a></span><span class="hspace"> </span><span class="RktSym">my-name</span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace"> </span><span class="RktMeta"><a href="http://docs.racket-lang.org/reference/stx-patterns.html#%28form._%28%28lib._racket%2Fprivate%2Fstxcase-scheme..rkt%29._......%29%29" class="RktStxLink" data-pltdoc="x">...</a></span><span class="RktPn">)</span><span class="RktPn">]</span><span class="RktPn">)</span><span class="RktPn">)</span><span class="RktPn">)</span><span class="RktPn">)</span></td></tr></table></blockquote><h4>2.5<tt> </tt><a name="(part._deleting-endpoints)"></a>Deleting endpoints</h4><p><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>procedure</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(def._((lib._marketplace/sugar-values..rkt)._delete-endpoint))"></a><span class="RktSym"><a href="high-level-interface.html#%28def._%28%28lib._marketplace%2Fsugar-values..rkt%29._delete-endpoint%29%29" class="RktValDef RktValLink" data-pltdoc="x">delete-endpoint</a></span><span class="hspace"> </span><span class="RktVar">id</span><span class="hspace"> </span>[<span class="RktVar">reason</span>]<span class="RktPn">)</span><span class="hspace"> </span>→<span class="hspace"> </span><span class="RktSym"><a href="low-level-interface.html#%28def._%28%28lib._marketplace%2Fmain..rkt%29._.Action%29%29" class="RktValLink" data-pltdoc="x">Action</a></span></p></blockquote></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">id</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym"><a href="http://docs.racket-lang.org/ts-reference/type-ref.html#%28form._%28%28lib._typed-racket%2Fbase-env%2Fbase-types..rkt%29._.Any%29%29" class="RktStxLink" data-pltdoc="x">Any</a></span></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">reason</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym"><a href="http://docs.racket-lang.org/ts-reference/type-ref.html#%28form._%28%28lib._typed-racket%2Fbase-env%2Fbase-types..rkt%29._.Any%29%29" class="RktStxLink" data-pltdoc="x">Any</a></span><span class="hspace"> </span>=<span class="hspace"> </span><span class="RktVal">#f</span></td></tr></table></blockquote></div><div class="SIntrapara">Use this action to delete a previously-added endpoint by name. The
|
|
<span class="RktVar">id</span> given must be <span class="RktSym"><a href="http://docs.racket-lang.org/reference/booleans.html#%28def._%28%28quote._~23~25kernel%29._equal~3f%29%29" class="RktValLink" data-pltdoc="x">equal?</a></span> to the corresponding
|
|
<span class="RktSym"><a href="low-level-interface.html#%28def._%28%28lib._marketplace%2Fmain..rkt%29._add-endpoint-pre-eid%29%29" class="RktValLink" data-pltdoc="x">add-endpoint-pre-eid</a></span>; when <span class="RktSym">endpoint</span> was used to
|
|
construct the endpoint to be deleted, the relevant name is that bound
|
|
by <span class="RktPn">#:let-name</span> or supplied to <span class="RktPn">#:name</span>. See
|
|
<a href="high-level-interface.html#%28part._naming-endpoints%29" data-pltdoc="x">Naming endpoints</a>.</div></p><p>If <span class="RktVar">reason</span> is supplied, it is included in the corresponding
|
|
action, and made available in any resulting <span class="RktSym"><a href="low-level-interface.html#%28def._%28%28lib._marketplace%2Fmain..rkt%29._absence-event%29%29" class="RktValLink" data-pltdoc="x">absence-event</a></span>s.</p><h4>2.6<tt> </tt><a name="(part._.Sending_messages_and_feedback)"></a>Sending messages and feedback</h4><p><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>procedure</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(def._((lib._marketplace/sugar-values..rkt)._send-message))"></a><span class="RktSym"><a href="high-level-interface.html#%28def._%28%28lib._marketplace%2Fsugar-values..rkt%29._send-message%29%29" class="RktValDef RktValLink" data-pltdoc="x">send-message</a></span><span class="hspace"> </span><span class="RktVar">body</span><span class="hspace"> </span>[<span class="RktVar">orientation</span>]<span class="RktPn">)</span><span class="hspace"> </span>→<span class="hspace"> </span><span class="RktSym"><a href="low-level-interface.html#%28def._%28%28lib._marketplace%2Fmain..rkt%29._.Action%29%29" class="RktValLink" data-pltdoc="x">Action</a></span></p></blockquote></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">body</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym"><a href="http://docs.racket-lang.org/ts-reference/type-ref.html#%28form._%28%28lib._typed-racket%2Fbase-env%2Fbase-types..rkt%29._.Any%29%29" class="RktStxLink" data-pltdoc="x">Any</a></span></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">orientation</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym"><a href="low-level-interface.html#%28def._%28%28lib._marketplace%2Fmain..rkt%29._.Orientation%29%29" class="RktValLink" data-pltdoc="x">Orientation</a></span><span class="hspace"> </span>=<span class="hspace"> </span><span class="RktVal">'</span><span class="RktVal">publisher</span></td></tr></table></blockquote></div><div class="SIntrapara">Constructs a message-sending action with the given orientation.
|
|
Usually the correct orientation to use is <span class="RktVal">'</span><span class="RktVal">publisher</span>; it
|
|
means that the sender of the message is acting in the "publisher"
|
|
role. Use <span class="RktVal">'</span><span class="RktVal">subscriber</span> instead when acting in the "subscriber"
|
|
role, i.e. sending feedback.</div></p><p><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>procedure</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(def._((lib._marketplace/sugar-values..rkt)._send-feedback))"></a><span class="RktSym"><a href="high-level-interface.html#%28def._%28%28lib._marketplace%2Fsugar-values..rkt%29._send-feedback%29%29" class="RktValDef RktValLink" data-pltdoc="x">send-feedback</a></span><span class="hspace"> </span><span class="RktVar">body</span><span class="RktPn">)</span><span class="hspace"> </span>→<span class="hspace"> </span><span class="RktSym"><a href="low-level-interface.html#%28def._%28%28lib._marketplace%2Fmain..rkt%29._.Action%29%29" class="RktValLink" data-pltdoc="x">Action</a></span></p></blockquote></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">body</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym"><a href="http://docs.racket-lang.org/ts-reference/type-ref.html#%28form._%28%28lib._typed-racket%2Fbase-env%2Fbase-types..rkt%29._.Any%29%29" class="RktStxLink" data-pltdoc="x">Any</a></span></td></tr></table></blockquote></div><div class="SIntrapara">Equivalent to <span class="RktPn">(</span><span class="RktSym"><a href="high-level-interface.html#%28def._%28%28lib._marketplace%2Fsugar-values..rkt%29._send-message%29%29" class="RktValLink" data-pltdoc="x">send-message</a></span><span class="stt"> </span><span class="RktVar">body</span><span class="stt"> </span><span class="RktVal">'</span><span class="RktVal">subscriber</span><span class="RktPn">)</span>.</div></p><h4>2.7<tt> </tt><a name="(part._.Creating_processes)"></a>Creating processes</h4><p><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" class="boxed RBoxed"><tr><td><table cellspacing="0" class="together"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>syntax</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(form._((lib._marketplace/sugar-untyped..rkt)._spawn))"></a><span class="RktSym"><a href="high-level-interface.html#%28form._%28%28lib._marketplace%2Fsugar-untyped..rkt%29._spawn%29%29" class="RktStxDef RktStxLink" data-pltdoc="x">spawn</a></span><span class="hspace"> </span><span class="RktVar">maybe-pid-binding</span><span class="hspace"> </span><span class="RktVar">boot-expr</span><span class="RktPn">)</span></p></blockquote></td></tr></table></td></tr><tr><td><table cellspacing="0" class="together"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>syntax</p></div></div><table cellspacing="0" class="RktBlk RForeground"><tr><td><span class="RktPn">(</span><a name="(form._((lib._marketplace/sugar-untyped..rkt)._spawn/continue))"></a><span class="RktSym"><a href="high-level-interface.html#%28form._%28%28lib._marketplace%2Fsugar-untyped..rkt%29._spawn%2Fcontinue%29%29" class="RktStxDef RktStxLink" data-pltdoc="x">spawn/continue</a></span><span class="hspace"> </span><span class="RktVar">maybe-pid-binding</span></td></tr><tr><td><span class="hspace"> </span><span class="RktPn">#:parent</span><span class="hspace"> </span><span class="RktVar">parent-state-pattern</span><span class="hspace"> </span><span class="RktVar">k-expr</span></td></tr><tr><td><span class="hspace"> </span><span class="RktPn">#:child</span><span class="hspace"> </span><span class="RktVar">boot-expr</span><span class="RktPn">)</span></td></tr></table></blockquote></td></tr></table></td></tr><tr><td><table cellspacing="0" class="together"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>syntax</p></div></div><table cellspacing="0" class="RktBlk RForeground"><tr><td><span class="RktPn">(</span><a name="(form._((lib._marketplace/sugar-typed..rkt)._spawn~3a))"></a><span class="RktSym"><a href="high-level-interface.html#%28form._%28%28lib._marketplace%2Fsugar-typed..rkt%29._spawn~3a%29%29" class="RktStxDef RktStxLink" data-pltdoc="x">spawn:</a></span><span class="hspace"> </span><span class="RktVar">maybe-pid-binding</span></td></tr><tr><td><span class="hspace"> </span><span class="RktPn">#:parent</span><span class="hspace"> </span><span class="RktSym"><a href="http://docs.racket-lang.org/ts-reference/special-forms.html#%28form._%28%28lib._typed-racket%2Fbase-env%2Fprims..rkt%29._~3a%29%29" class="RktStxLink" data-pltdoc="x">:</a></span><span class="hspace"> </span><span class="RktVar">ParentStateType</span></td></tr><tr><td><span class="hspace"> </span><span class="RktPn">#:child</span><span class="hspace"> </span><span class="RktSym"><a href="http://docs.racket-lang.org/ts-reference/special-forms.html#%28form._%28%28lib._typed-racket%2Fbase-env%2Fprims..rkt%29._~3a%29%29" class="RktStxLink" data-pltdoc="x">:</a></span><span class="hspace"> </span><span class="RktVar">ChildStateType</span><span class="hspace"> </span><span class="RktVar">boot-expr</span><span class="RktPn">)</span></td></tr></table></blockquote></td></tr></table></td></tr><tr><td><table cellspacing="0" class="together"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>syntax</p></div></div><table cellspacing="0" class="RktBlk RForeground"><tr><td><span class="RktPn">(</span><a name="(form._((lib._marketplace/sugar-typed..rkt)._spawn/continue~3a))"></a><span class="RktSym"><a href="high-level-interface.html#%28form._%28%28lib._marketplace%2Fsugar-typed..rkt%29._spawn%2Fcontinue~3a%29%29" class="RktStxDef RktStxLink" data-pltdoc="x">spawn/continue:</a></span><span class="hspace"> </span><span class="RktVar">maybe-pid-binding</span></td></tr><tr><td><span class="hspace"> </span><span class="RktPn">#:parent</span><span class="hspace"> </span><span class="RktVar">parent-state-pattern</span><span class="hspace"> </span><span class="RktSym"><a href="http://docs.racket-lang.org/ts-reference/special-forms.html#%28form._%28%28lib._typed-racket%2Fbase-env%2Fprims..rkt%29._~3a%29%29" class="RktStxLink" data-pltdoc="x">:</a></span><span class="hspace"> </span><span class="RktVar">ParentStateType</span><span class="hspace"> </span><span class="RktVar">k-expr</span></td></tr><tr><td><span class="hspace"> </span><span class="RktPn">#:child</span><span class="hspace"> </span><span class="RktSym"><a href="http://docs.racket-lang.org/ts-reference/special-forms.html#%28form._%28%28lib._typed-racket%2Fbase-env%2Fprims..rkt%29._~3a%29%29" class="RktStxLink" data-pltdoc="x">:</a></span><span class="hspace"> </span><span class="RktVar">ChildStateType</span><span class="hspace"> </span><span class="RktVar">boot-expr</span><span class="RktPn">)</span></td></tr></table></blockquote></td></tr><tr><td><span class="stt"> </span></td></tr><tr><td><table cellspacing="0" class="specgrammar"><tr><td align="right" valign="baseline"><span class="RktVar">maybe-pid-binding</span></td><td align="left" valign="baseline"><span class="stt"> </span></td><td align="center" valign="baseline">=</td><td align="left" valign="baseline"><span class="stt"> </span></td><td align="left" valign="baseline"><table cellspacing="0" class="RktBlk"><tr><td></td></tr></table></td></tr><tr><td align="right" valign="baseline"><span class="stt"> </span></td><td align="left" valign="baseline"><span class="stt"> </span></td><td align="center" valign="baseline">|</td><td align="left" valign="baseline"><span class="stt"> </span></td><td align="left" valign="baseline"><span class="RktPn">#:pid</span><span class="hspace"> </span><span class="RktVar">identifier</span></td></tr><tr><td align="right" valign="baseline"><span class="stt"> </span></td><td align="left" valign="baseline"><span class="stt"> </span></td><td align="center" valign="baseline"><span class="stt"> </span></td><td align="left" valign="baseline"><span class="stt"> </span></td><td align="left" valign="baseline"><span class="stt"> </span></td></tr><tr><td align="right" valign="baseline"><span class="RktVar">k-expr</span></td><td align="left" valign="baseline"><span class="stt"> </span></td><td align="center" valign="baseline">=</td><td align="left" valign="baseline"><span class="stt"> </span></td><td align="left" valign="baseline"><span class="RktVar">expr</span></td></tr><tr><td align="right" valign="baseline"><span class="stt"> </span></td><td align="left" valign="baseline"><span class="stt"> </span></td><td align="center" valign="baseline"><span class="stt"> </span></td><td align="left" valign="baseline"><span class="stt"> </span></td><td align="left" valign="baseline"><span class="stt"> </span></td></tr><tr><td align="right" valign="baseline"><span class="RktVar">boot-expr</span></td><td align="left" valign="baseline"><span class="stt"> </span></td><td align="center" valign="baseline">=</td><td align="left" valign="baseline"><span class="stt"> </span></td><td align="left" valign="baseline"><span class="RktVar">expr</span></td></tr></table></td></tr></table></td></tr></table></blockquote></div><div class="SIntrapara">Action describing a new process to create. The <span class="RktVar">boot-expr</span>
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should be an expression yielding a <span class="RktSym"><a href="high-level-interface.html#%28form._%28%28lib._marketplace%2Fsugar-values..rkt%29._transition%29%29" class="RktStxLink" data-pltdoc="x">transition</a></span> that contains
|
|
the child process’s initial state and initial actions.</div></p><p>If <span class="RktPn">#:pid</span> is supplied, the associated identifier is bound to
|
|
the child process’s PID in both <span class="RktVar">boot-expr</span> and the parent’s
|
|
<span class="RktVar">k-expr</span>.</p><p>The <span class="RktSym"><a href="high-level-interface.html#%28form._%28%28lib._marketplace%2Fsugar-untyped..rkt%29._spawn%2Fcontinue%29%29" class="RktStxLink" data-pltdoc="x">spawn/continue</a></span> and <span class="RktSym"><a href="high-level-interface.html#%28form._%28%28lib._marketplace%2Fsugar-typed..rkt%29._spawn%2Fcontinue~3a%29%29" class="RktStxLink" data-pltdoc="x">spawn/continue:</a></span> variations
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|
include a <span class="RktVar">k-expr</span>, which will run in the parent process after
|
|
the child process has been created. Note that <span class="RktVar">k-expr</span> must
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return a <span class="RktSym"><a href="high-level-interface.html#%28def._%28%28lib._marketplace%2Fmain..rkt%29._.Transition%29%29" class="RktValLink" data-pltdoc="x">Transition</a></span>, since <span class="RktVar">parent-state-pattern</span> is
|
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always supplied for these variations.</p><p>In Typed Racket, for type system reasons, <span class="RktSym"><a href="high-level-interface.html#%28form._%28%28lib._marketplace%2Fsugar-typed..rkt%29._spawn~3a%29%29" class="RktStxLink" data-pltdoc="x">spawn:</a></span> and
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<span class="RktSym"><a href="high-level-interface.html#%28form._%28%28lib._marketplace%2Fsugar-typed..rkt%29._spawn%2Fcontinue~3a%29%29" class="RktStxLink" data-pltdoc="x">spawn/continue:</a></span> require <span class="RktVar">ParentStateType</span> to be
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supplied as well as <span class="RktVar">ChildStateType</span>.</p><p><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>procedure</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(def._((lib._marketplace/sugar-typed..rkt)._name-process))"></a><span class="RktSym"><a href="high-level-interface.html#%28def._%28%28lib._marketplace%2Fsugar-typed..rkt%29._name-process%29%29" class="RktValDef RktValLink" data-pltdoc="x">name-process</a></span><span class="hspace"> </span><span class="RktVar">id</span><span class="hspace"> </span><span class="RktVar">spawn-action</span><span class="RktPn">)</span><span class="hspace"> </span>→<span class="hspace"> </span><span class="RktSym"><a href="low-level-interface.html#%28def._%28%28lib._marketplace%2Fmain..rkt%29._.Spawn%29%29" class="RktValLink" data-pltdoc="x">Spawn</a></span></p></blockquote></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">id</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym"><a href="http://docs.racket-lang.org/ts-reference/type-ref.html#%28form._%28%28lib._typed-racket%2Fbase-env%2Fbase-types..rkt%29._.Any%29%29" class="RktStxLink" data-pltdoc="x">Any</a></span></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">spawn-action</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym"><a href="low-level-interface.html#%28def._%28%28lib._marketplace%2Fmain..rkt%29._.Spawn%29%29" class="RktValLink" data-pltdoc="x">Spawn</a></span></td></tr></table></blockquote></div><div class="SIntrapara">Returns a copy of the passed-in <span class="RktSym"><a href="high-level-interface.html#%28form._%28%28lib._marketplace%2Fsugar-untyped..rkt%29._spawn%29%29" class="RktStxLink" data-pltdoc="x">spawn</a></span> action structure, with
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the <span class="RktSym">debug-name</span> field set to the passed-in identifying value.
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|
The debug name of a process is used in VM debug output. See also
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<a href="Management_and_Monitoring.html#%28part._logging%29" data-pltdoc="x">logging (MARKETPLACE_LOG)</a>.</div></p><h4>2.8<tt> </tt><a name="(part._.Exiting_and_killing_processes)"></a>Exiting and killing processes</h4><p><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>procedure</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(def._((lib._marketplace/sugar-values..rkt)._quit))"></a><span class="RktSym"><a href="high-level-interface.html#%28def._%28%28lib._marketplace%2Fsugar-values..rkt%29._quit%29%29" class="RktValDef RktValLink" data-pltdoc="x">quit</a></span><span class="hspace"> </span>[<span class="RktVar">who</span><span class="hspace"> </span><span class="RktVar">reason</span>]<span class="RktPn">)</span><span class="hspace"> </span>→<span class="hspace"> </span><span class="RktSym"><a href="low-level-interface.html#%28def._%28%28lib._marketplace%2Fmain..rkt%29._.Action%29%29" class="RktValLink" data-pltdoc="x">Action</a></span></p></blockquote></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">who</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="http://docs.racket-lang.org/ts-reference/type-ref.html#%28form._%28%28lib._typed-racket%2Fbase-env%2Fbase-types..rkt%29._.Option%29%29" class="RktStxLink" data-pltdoc="x">Option</a></span><span class="hspace"> </span><span class="RktSym"><a href="low-level-interface.html#%28def._%28%28lib._marketplace%2Fmain..rkt%29._.P.I.D%29%29" class="RktValLink" data-pltdoc="x">PID</a></span><span class="RktPn">)</span><span class="hspace"> </span>=<span class="hspace"> </span><span class="RktVal">#f</span></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">reason</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym"><a href="http://docs.racket-lang.org/ts-reference/type-ref.html#%28form._%28%28lib._typed-racket%2Fbase-env%2Fbase-types..rkt%29._.Any%29%29" class="RktStxLink" data-pltdoc="x">Any</a></span><span class="hspace"> </span>=<span class="hspace"> </span><span class="RktVal">#f</span></td></tr></table></blockquote></div><div class="SIntrapara">Action causing the termination of a process. If <span class="RktVar">who</span> is
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|
omitted or <span class="RktVal">#f</span>, terminates the acting process; otherwise,
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|
terminates the peer process having <span class="RktVar">who</span> as its PID.</div></p><p>If <span class="RktVar">reason</span> is supplied, it is included in the corresponding
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action, and made available in any resulting <span class="RktSym"><a href="low-level-interface.html#%28def._%28%28lib._marketplace%2Fmain..rkt%29._absence-event%29%29" class="RktValLink" data-pltdoc="x">absence-event</a></span>s.</p><p>Terminating the current process is as simple as:</p><blockquote class="SCodeFlow"><p><span class="RktPn">(</span><span class="RktSym"><a href="high-level-interface.html#%28def._%28%28lib._marketplace%2Fsugar-values..rkt%29._quit%29%29" class="RktValLink" data-pltdoc="x">quit</a></span><span class="RktPn">)</span></p></blockquote><p>When a process raises an exception that it does not catch, its
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|
containing VM catches the exception and turns it into an implicit quit
|
|
action. In that case, the <span class="RktVar">reason</span> will be the raised exception
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itself.</p><h4>2.9<tt> </tt><a name="(part._.Cooperative_scheduling)"></a>Cooperative scheduling</h4><p><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" class="boxed RBoxed"><tr><td><table cellspacing="0" class="together"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>syntax</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(form._((lib._marketplace/sugar-untyped..rkt)._yield))"></a><span class="RktSym"><a href="high-level-interface.html#%28form._%28%28lib._marketplace%2Fsugar-untyped..rkt%29._yield%29%29" class="RktStxDef RktStxLink" data-pltdoc="x">yield</a></span><span class="hspace"> </span><span class="RktVar">state-pattern</span><span class="hspace"> </span><span class="RktVar">k-expr</span><span class="RktPn">)</span></p></blockquote></td></tr></table></td></tr><tr><td><table cellspacing="0" class="together"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>syntax</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(form._((lib._marketplace/sugar-typed..rkt)._yield~3a))"></a><span class="RktSym"><a href="high-level-interface.html#%28form._%28%28lib._marketplace%2Fsugar-typed..rkt%29._yield~3a%29%29" class="RktStxDef RktStxLink" data-pltdoc="x">yield:</a></span><span class="hspace"> </span><span class="RktVar">state-pattern</span><span class="hspace"> </span><span class="RktSym"><a href="http://docs.racket-lang.org/ts-reference/special-forms.html#%28form._%28%28lib._typed-racket%2Fbase-env%2Fprims..rkt%29._~3a%29%29" class="RktStxLink" data-pltdoc="x">:</a></span><span class="hspace"> </span><span class="RktVar">State</span><span class="hspace"> </span><span class="RktVar">k-expr</span><span class="RktPn">)</span></p></blockquote></td></tr></table></td></tr></table></blockquote></div><div class="SIntrapara">Lets other processes in the system run for a step, returning to
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|
evaluate <span class="RktVar">k-expr</span> only after doing a complete round of the
|
|
scheduler.</div></p><p>The state of the yielding process will be matched against
|
|
<span class="RktVar">state-pattern</span> when the process is resumed, and
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<span class="RktVar">k-expr</span> must evaluate to a <span class="RktSym"><a href="high-level-interface.html#%28def._%28%28lib._marketplace%2Fmain..rkt%29._.Transition%29%29" class="RktValLink" data-pltdoc="x">Transition</a></span>.</p><h4>2.10<tt> </tt><a name="(part._.Creating_nested_.V.Ms)"></a>Creating nested VMs</h4><p><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" class="boxed RBoxed"><tr><td><table cellspacing="0" class="together"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>syntax</p></div></div><table cellspacing="0" class="RktBlk RForeground"><tr><td><span class="RktPn">(</span><a name="(form._((lib._marketplace/sugar-untyped..rkt)._spawn-vm))"></a><span class="RktSym"><a href="high-level-interface.html#%28form._%28%28lib._marketplace%2Fsugar-untyped..rkt%29._spawn-vm%29%29" class="RktStxDef RktStxLink" data-pltdoc="x">spawn-vm</a></span><span class="hspace"> </span><span class="RktVar">maybe-vm-pid-binding</span><span class="hspace"> </span><span class="RktVar">maybe-boot-pid-binding</span></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">maybe-initial-state</span></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">maybe-debug-name</span></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">boot-action-expr</span><span class="hspace"> </span><span class="RktMeta">...</span><span class="RktPn">)</span></td></tr></table></blockquote></td></tr></table></td></tr><tr><td><table cellspacing="0" class="together"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>syntax</p></div></div><table cellspacing="0" class="RktBlk RForeground"><tr><td><span class="RktPn">(</span><a name="(form._((lib._marketplace/sugar-typed..rkt)._spawn-vm~3a))"></a><span class="RktSym"><a href="high-level-interface.html#%28form._%28%28lib._marketplace%2Fsugar-typed..rkt%29._spawn-vm~3a%29%29" class="RktStxDef RktStxLink" data-pltdoc="x">spawn-vm:</a></span><span class="hspace"> </span><span class="RktSym"><a href="http://docs.racket-lang.org/ts-reference/special-forms.html#%28form._%28%28lib._typed-racket%2Fbase-env%2Fprims..rkt%29._~3a%29%29" class="RktStxLink" data-pltdoc="x">:</a></span><span class="hspace"> </span><span class="RktVar">ParentStateType</span></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">maybe-vm-pid-binding</span><span class="hspace"> </span><span class="RktVar">maybe-boot-pid-binding</span></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">maybe-typed-initial-state</span></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">maybe-debug-name</span></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">boot-action-expr</span><span class="hspace"> </span><span class="RktMeta">...</span><span class="RktPn">)</span></td></tr></table></blockquote></td></tr><tr><td><span class="stt"> </span></td></tr><tr><td><table cellspacing="0" class="specgrammar"><tr><td align="right" valign="baseline"><span class="RktVar">maybe-vm-pid-binding</span></td><td align="left" valign="baseline"><span class="stt"> </span></td><td align="center" valign="baseline">=</td><td align="left" valign="baseline"><span class="stt"> </span></td><td align="left" valign="baseline"><table cellspacing="0" class="RktBlk"><tr><td></td></tr></table></td></tr><tr><td align="right" valign="baseline"><span class="stt"> </span></td><td align="left" valign="baseline"><span class="stt"> </span></td><td align="center" valign="baseline">|</td><td align="left" valign="baseline"><span class="stt"> </span></td><td align="left" valign="baseline"><span class="RktPn">#:vm-pid</span><span class="hspace"> </span><span class="RktVar">identifier</span></td></tr><tr><td align="right" valign="baseline"><span class="stt"> </span></td><td align="left" valign="baseline"><span class="stt"> </span></td><td align="center" valign="baseline"><span class="stt"> </span></td><td align="left" valign="baseline"><span class="stt"> </span></td><td align="left" valign="baseline"><span class="stt"> </span></td></tr><tr><td align="right" valign="baseline"><span class="RktVar">maybe-boot-pid-binding</span></td><td align="left" valign="baseline"><span class="stt"> </span></td><td align="center" valign="baseline">=</td><td align="left" valign="baseline"><span class="stt"> </span></td><td align="left" valign="baseline"><table cellspacing="0" class="RktBlk"><tr><td></td></tr></table></td></tr><tr><td align="right" valign="baseline"><span class="stt"> </span></td><td align="left" valign="baseline"><span class="stt"> </span></td><td align="center" valign="baseline">|</td><td align="left" valign="baseline"><span class="stt"> </span></td><td align="left" valign="baseline"><span class="RktPn">#:boot-pid</span><span class="hspace"> </span><span class="RktVar">identifier</span></td></tr><tr><td align="right" valign="baseline"><span class="stt"> </span></td><td align="left" valign="baseline"><span class="stt"> </span></td><td align="center" valign="baseline"><span class="stt"> </span></td><td align="left" valign="baseline"><span class="stt"> </span></td><td align="left" valign="baseline"><span class="stt"> </span></td></tr><tr><td align="right" valign="baseline"><span class="RktVar">maybe-initial-state</span></td><td align="left" valign="baseline"><span class="stt"> </span></td><td align="center" valign="baseline">=</td><td align="left" valign="baseline"><span class="stt"> </span></td><td align="left" valign="baseline"><table cellspacing="0" class="RktBlk"><tr><td></td></tr></table></td></tr><tr><td align="right" valign="baseline"><span class="stt"> </span></td><td align="left" valign="baseline"><span class="stt"> </span></td><td align="center" valign="baseline">|</td><td align="left" valign="baseline"><span class="stt"> </span></td><td align="left" valign="baseline"><span class="RktPn">#:initial-state</span><span class="hspace"> </span><span class="RktVar">expr</span></td></tr><tr><td align="right" valign="baseline"><span class="stt"> </span></td><td align="left" valign="baseline"><span class="stt"> </span></td><td align="center" valign="baseline"><span class="stt"> </span></td><td align="left" valign="baseline"><span class="stt"> </span></td><td align="left" valign="baseline"><span class="stt"> </span></td></tr><tr><td align="right" valign="baseline"><span class="RktVar">maybe-typed-initial-state</span></td><td align="left" valign="baseline"><span class="stt"> </span></td><td align="center" valign="baseline">=</td><td align="left" valign="baseline"><span class="stt"> </span></td><td align="left" valign="baseline"><table cellspacing="0" class="RktBlk"><tr><td></td></tr></table></td></tr><tr><td align="right" valign="baseline"><span class="stt"> </span></td><td align="left" valign="baseline"><span class="stt"> </span></td><td align="center" valign="baseline">|</td><td align="left" valign="baseline"><span class="stt"> </span></td><td align="left" valign="baseline"><span class="RktPn">#:initial-state</span><span class="hspace"> </span><span class="RktVar">expr</span><span class="hspace"> </span><span class="RktSym"><a href="http://docs.racket-lang.org/ts-reference/special-forms.html#%28form._%28%28lib._typed-racket%2Fbase-env%2Fprims..rkt%29._~3a%29%29" class="RktStxLink" data-pltdoc="x">:</a></span><span class="hspace"> </span><span class="RktVar">StateType</span></td></tr><tr><td align="right" valign="baseline"><span class="stt"> </span></td><td align="left" valign="baseline"><span class="stt"> </span></td><td align="center" valign="baseline"><span class="stt"> </span></td><td align="left" valign="baseline"><span class="stt"> </span></td><td align="left" valign="baseline"><span class="stt"> </span></td></tr><tr><td align="right" valign="baseline"><span class="RktVar">maybe-debug-name</span></td><td align="left" valign="baseline"><span class="stt"> </span></td><td align="center" valign="baseline">=</td><td align="left" valign="baseline"><span class="stt"> </span></td><td align="left" valign="baseline"><table cellspacing="0" class="RktBlk"><tr><td></td></tr></table></td></tr><tr><td align="right" valign="baseline"><span class="stt"> </span></td><td align="left" valign="baseline"><span class="stt"> </span></td><td align="center" valign="baseline">|</td><td align="left" valign="baseline"><span class="stt"> </span></td><td align="left" valign="baseline"><span class="RktPn">#:debug-name</span><span class="hspace"> </span><span class="RktVar">expr</span></td></tr><tr><td align="right" valign="baseline"><span class="stt"> </span></td><td align="left" valign="baseline"><span class="stt"> </span></td><td align="center" valign="baseline"><span class="stt"> </span></td><td align="left" valign="baseline"><span class="stt"> </span></td><td align="left" valign="baseline"><span class="stt"> </span></td></tr><tr><td align="right" valign="baseline"><span class="RktVar">boot-action-expr</span></td><td align="left" valign="baseline"><span class="stt"> </span></td><td align="center" valign="baseline">=</td><td align="left" valign="baseline"><span class="stt"> </span></td><td align="left" valign="baseline"><span class="RktVar">expr</span></td></tr></table></td></tr></table></td></tr></table></blockquote></div><div class="SIntrapara">Results in a <span class="RktSym"><a href="high-level-interface.html#%28form._%28%28lib._marketplace%2Fsugar-untyped..rkt%29._spawn%29%29" class="RktStxLink" data-pltdoc="x">spawn</a></span> action that starts a nested VM. The
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primordial process in the new VM executes the boot-actions with the
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given initial state. (If no initial state is supplied, <span class="RktPn">(</span><span class="RktSym"><a href="http://docs.racket-lang.org/reference/void.html#%28def._%28%28quote._~23~25kernel%29._void%29%29" class="RktValLink" data-pltdoc="x">void</a></span><span class="RktPn">)</span>
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is used.)</div></p><p>If <span class="RktPn">#:vm-pid</span> is present, the corresponding identifier is bound
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in the boot-action expressions to the container-relative PID of the
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new VM itself. If <span class="RktPn">#:boot-pid</span> is present, however, the
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corresponding identifier is bound to the new-VM-relative PID of the
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primordial process in the new VM.</p><h4>2.11<tt> </tt><a name="(part._.Relaying_across_layers)"></a>Relaying across layers</h4><p><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" class="boxed RBoxed"><tr><td><table cellspacing="0" class="together"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>syntax</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(form._((lib._marketplace/sugar-typed..rkt)._at-meta-level~3a))"></a><span class="RktSym"><a href="high-level-interface.html#%28form._%28%28lib._marketplace%2Fsugar-typed..rkt%29._at-meta-level~3a%29%29" class="RktStxDef RktStxLink" data-pltdoc="x">at-meta-level:</a></span><span class="hspace"> </span><span class="RktVar">StateType</span><span class="hspace"> </span><span class="RktVar">preaction</span><span class="hspace"> </span><span class="RktMeta">...</span><span class="RktPn">)</span></p></blockquote></td></tr></table></td></tr><tr><td><table cellspacing="0" class="together"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>procedure</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(def._((lib._marketplace/sugar-untyped..rkt)._at-meta-level))"></a><span class="RktSym"><a href="high-level-interface.html#%28def._%28%28lib._marketplace%2Fsugar-untyped..rkt%29._at-meta-level%29%29" class="RktValDef RktValLink" data-pltdoc="x">at-meta-level</a></span><span class="hspace"> </span><span class="RktVar">preaction</span><span class="hspace"> </span><span class="RktMeta">...</span><span class="RktPn">)</span><span class="hspace"> </span>→<span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="low-level-interface.html#%28def._%28%28lib._marketplace%2Fmain..rkt%29._.Action%29%29" class="RktValLink" data-pltdoc="x">Action</a></span><span class="hspace"> </span><span class="RktVar">StateType</span><span class="RktPn">)</span></p></blockquote></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">preaction</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="low-level-interface.html#%28def._%28%28lib._marketplace%2Fmain..rkt%29._.Pre.Action%29%29" class="RktValLink" data-pltdoc="x">PreAction</a></span><span class="hspace"> </span><span class="RktSym">State</span><span class="RktPn">)</span></td></tr></table></td></tr></table></blockquote></div><div class="SIntrapara">Each VM gives its processes access to two distinct IPC facilities: the
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<span style="font-style: italic">internal</span> one, provided for the VM’s processes to talk amongst
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themselves, and the <span style="font-style: italic">external</span> one, the network that the VM
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itself is a process within.</div></p><p>Marketplace’s actions can apply to either of those two networks. By
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default, actions apply to the VM of the acting process directly, but
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using <span class="RktSym"><a href="high-level-interface.html#%28def._%28%28lib._marketplace%2Fsugar-untyped..rkt%29._at-meta-level%29%29" class="RktValLink" data-pltdoc="x">at-meta-level</a></span> (or <span class="RktSym"><a href="high-level-interface.html#%28form._%28%28lib._marketplace%2Fsugar-typed..rkt%29._at-meta-level~3a%29%29" class="RktStxLink" data-pltdoc="x">at-meta-level:</a></span> in typed
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code) to wrap an action <span style="font-style: italic">level-shifts</span> the action to make it
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apply at the level of the acting process’s VM’s container instead.</p><p>For example, wrapping an <span class="RktSym">endpoint</span> in <span class="RktSym"><a href="high-level-interface.html#%28def._%28%28lib._marketplace%2Fsugar-untyped..rkt%29._at-meta-level%29%29" class="RktValLink" data-pltdoc="x">at-meta-level</a></span>
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adds a subscription to the VM’s container’s network. Instead of
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listening to sibling processes of the acting process, the new endpoint
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will listen to sibling processes of the acting process’s VM. In this
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example, the primordial process in the nested VM creates an
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endpoint in the VM’s own network, the ground VM:</p><blockquote class="SCodeFlow"><table cellspacing="0" class="RktBlk"><tr><td><span class="RktPn">(</span><span class="RktSym"><a href="high-level-interface.html#%28form._%28%28lib._marketplace%2Fsugar-untyped..rkt%29._spawn-vm%29%29" class="RktStxLink" data-pltdoc="x">spawn-vm</a></span></td></tr><tr><td><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="high-level-interface.html#%28def._%28%28lib._marketplace%2Fsugar-untyped..rkt%29._at-meta-level%29%29" class="RktValLink" data-pltdoc="x">at-meta-level</a></span></td></tr><tr><td><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="high-level-interface.html#%28form._%28%28lib._marketplace%2Fsugar-untyped..rkt%29._subscriber%29%29" class="RktStxLink" data-pltdoc="x">subscriber</a></span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym">tcp-channel</span><span class="hspace"> </span><span class="RktSym"><a href="low-level-interface.html#%28def._%28%28lib._marketplace%2Fsugar-untyped..rkt%29._~3f%29%29" class="RktValLink" data-pltdoc="x">?</a></span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym">tcp-listener</span><span class="hspace"> </span><span class="RktVal">5999</span><span class="RktPn">)</span><span class="hspace"> </span><span class="RktSym"><a href="low-level-interface.html#%28def._%28%28lib._marketplace%2Fsugar-untyped..rkt%29._~3f%29%29" class="RktValLink" data-pltdoc="x">?</a></span><span class="RktPn">)</span><span class="hspace"> </span><span class="RktSym"><a href="http://docs.racket-lang.org/reference/stx-patterns.html#%28form._%28%28lib._racket%2Fprivate%2Fstxcase-scheme..rkt%29._......%29%29" class="RktStxLink" data-pltdoc="x">...</a></span><span class="RktPn">)</span><span class="RktPn">)</span><span class="RktPn">)</span></td></tr></table></blockquote><p>In this example, a new process is spawned as a sibling of the
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nested VM rather than as a sibling of its primordial process:</p><blockquote class="SCodeFlow"><table cellspacing="0" class="RktBlk"><tr><td><span class="RktPn">(</span><span class="RktSym"><a href="high-level-interface.html#%28form._%28%28lib._marketplace%2Fsugar-untyped..rkt%29._spawn-vm%29%29" class="RktStxLink" data-pltdoc="x">spawn-vm</a></span></td></tr><tr><td><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="high-level-interface.html#%28def._%28%28lib._marketplace%2Fsugar-untyped..rkt%29._at-meta-level%29%29" class="RktValLink" data-pltdoc="x">at-meta-level</a></span></td></tr><tr><td><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="high-level-interface.html#%28form._%28%28lib._marketplace%2Fsugar-untyped..rkt%29._spawn%29%29" class="RktStxLink" data-pltdoc="x">spawn</a></span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="high-level-interface.html#%28form._%28%28lib._marketplace%2Fsugar-typed..rkt%29._transition%2Fno-state%29%29" class="RktStxLink" data-pltdoc="x">transition/no-state</a></span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="high-level-interface.html#%28def._%28%28lib._marketplace%2Fsugar-values..rkt%29._send-message%29%29" class="RktValLink" data-pltdoc="x">send-message</a></span><span class="hspace"> </span><span class="RktVal">'</span><span class="RktVal">hello-world</span><span class="RktPn">)</span><span class="RktPn">)</span><span class="RktPn">)</span><span class="RktPn">)</span><span class="RktPn">)</span></td></tr></table></blockquote><p>Compare to this example, which spawns a sibling of the
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nested VM’s primordial process:</p><blockquote class="SCodeFlow"><table cellspacing="0" class="RktBlk"><tr><td><span class="RktPn">(</span><span class="RktSym"><a href="high-level-interface.html#%28form._%28%28lib._marketplace%2Fsugar-untyped..rkt%29._spawn-vm%29%29" class="RktStxLink" data-pltdoc="x">spawn-vm</a></span></td></tr><tr><td><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="high-level-interface.html#%28form._%28%28lib._marketplace%2Fsugar-untyped..rkt%29._spawn%29%29" class="RktStxLink" data-pltdoc="x">spawn</a></span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="high-level-interface.html#%28form._%28%28lib._marketplace%2Fsugar-typed..rkt%29._transition%2Fno-state%29%29" class="RktStxLink" data-pltdoc="x">transition/no-state</a></span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="high-level-interface.html#%28def._%28%28lib._marketplace%2Fsugar-values..rkt%29._send-message%29%29" class="RktValLink" data-pltdoc="x">send-message</a></span><span class="hspace"> </span><span class="RktVal">'</span><span class="RktVal">hello-world</span><span class="RktPn">)</span><span class="RktPn">)</span><span class="RktPn">)</span><span class="RktPn">)</span></td></tr></table></blockquote><div class="navsetbottom"><span class="navleft"> </span><span class="navright"> <a href="Concepts.html" title="backward to "1 Concepts"" data-pltdoc="x">← prev</a> <a href="index.html" title="up to "Marketplace: Network-Aware Programming"" data-pltdoc="x">up</a> <a href="low-level-interface.html" title="forward to "3 Low-level interface"" data-pltdoc="x">next →</a></span> </div></div></div><div id="contextindicator"> </div></body></html> |