171 lines
145 KiB
HTML
171 lines
145 KiB
HTML
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
|
|
<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="scribble-style.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" style="margin-bottom: 1em;"><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="" 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="" 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="#%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="#%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="#%28part._constructing-transitions%29" class="tocviewlink" data-pltdoc="x">Constructing transitions</a></td></tr><tr><td align="right">2.4 </td><td><a href="#%28part._endpoint-dsl%29" class="tocviewlink" data-pltdoc="x">Creating endpoints</a></td></tr><tr><td align="right">2.5 </td><td><a href="#%28part._deleting-endpoints%29" class="tocviewlink" data-pltdoc="x">Deleting endpoints</a></td></tr><tr><td align="right">2.6 </td><td><a href="#%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="#%28part._.Creating_processes%29" class="tocviewlink" data-pltdoc="x">Creating processes</a></td></tr><tr><td align="right">2.8 </td><td><a href="#%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="#%28part._.Cooperative_scheduling%29" class="tocviewlink" data-pltdoc="x">Cooperative scheduling</a></td></tr><tr><td align="right">2.10 </td><td><a href="#%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="#%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="#(part._hashlang-variations)" 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="#(part._.Using_.Marketplace_as_a_library)" class="tocsubseclink" data-pltdoc="x">Using Marketplace as a library</a></td></tr><tr><td><a href="#(form._((lib._marketplace/sugar-untyped..rkt)._ground-vm))" class="tocsubnonseclink" data-pltdoc="x"><span title="Provided from: marketplace/sugar-untyped, marketplace/sugar-typed"><span class="RktSym"><span class="badlink"><span class="RktValLink">ground-<wbr></wbr>vm</span></span></span></span></a></td></tr><tr><td><a href="#(form._((lib._marketplace/sugar-untyped..rkt)._ground-vm~3a))" class="tocsubnonseclink" data-pltdoc="x"><span title="Provided from: marketplace/sugar-untyped, marketplace/sugar-typed"><span class="RktSym"><span class="badlink"><span class="RktValLink">ground-<wbr></wbr>vm:</span></span></span></span></a></td></tr><tr><td><span class="tocsublinknumber">2.3<tt> </tt></span><a href="#(part._constructing-transitions)" class="tocsubseclink" data-pltdoc="x">Constructing transitions</a></td></tr><tr><td><span class="tocsublinknumber">2.4<tt> </tt></span><a href="#(part._endpoint-dsl)" class="tocsubseclink" data-pltdoc="x">Creating endpoints</a></td></tr><tr><td><span class="tocsublinknumber">2.4.1<tt> </tt></span><a href="#(part._.Receiving_messages)" class="tocsubseclink" data-pltdoc="x">Receiving messages</a></td></tr><tr><td><span class="tocsublinknumber">2.4.2<tt> </tt></span><a href="#(part._.Action-only_vs__.State_updates)" class="tocsubseclink" data-pltdoc="x">Action-<wbr></wbr>only vs. State updates</a></td></tr><tr><td><span class="tocsublinknumber">2.4.3<tt> </tt></span><a href="#(part._naming-endpoints)" class="tocsubseclink" data-pltdoc="x">Naming endpoints</a></td></tr><tr><td><span class="tocsublinknumber">2.4.4<tt> </tt></span><a href="#(part._.Handling_presence_and_absence_events)" class="tocsubseclink" data-pltdoc="x">Handling presence and absence events</a></td></tr><tr><td><span class="tocsublinknumber">2.4.5<tt> </tt></span><a href="#(part._.Exit_reasons)" class="tocsubseclink" data-pltdoc="x">Exit reasons</a></td></tr><tr><td><span class="tocsublinknumber">2.4.6<tt> </tt></span><a href="#(part._updating-endpoints)" class="tocsubseclink" data-pltdoc="x">Updating endpoints</a></td></tr><tr><td><span class="tocsublinknumber">2.4.7<tt> </tt></span><a href="#(part._.Who_am_.I_talking_to_)" class="tocsubseclink" data-pltdoc="x">Who am I talking to?</a></td></tr><tr><td><span class="tocsublinknumber">2.5<tt> </tt></span><a href="#(part._deleting-endpoints)" class="tocsubseclink" data-pltdoc="x">Deleting endpoints</a></td></tr><tr><td><span class="tocsublinknumber">2.6<tt> </tt></span><a href="#(part._.Sending_messages_and_feedback)" class="tocsubseclink" data-pltdoc="x">Sending messages and feedback</a></td></tr><tr><td><span class="tocsublinknumber">2.7<tt> </tt></span><a href="#(part._.Creating_processes)" class="tocsubseclink" data-pltdoc="x">Creating processes</a></td></tr><tr><td><span class="tocsublinknumber">2.8<tt> </tt></span><a href="#(part._.Exiting_and_killing_processes)" class="tocsubseclink" data-pltdoc="x">Exiting and killing processes</a></td></tr><tr><td><span class="tocsublinknumber">2.9<tt> </tt></span><a href="#(part._.Cooperative_scheduling)" class="tocsubseclink" data-pltdoc="x">Cooperative scheduling</a></td></tr><tr><td><span class="tocsublinknumber">2.10<tt> </tt></span><a href="#(part._.Creating_nested_.V.Ms)" class="tocsubseclink" data-pltdoc="x">Creating nested VMs</a></td></tr><tr><td><span class="tocsublinknumber">2.11<tt> </tt></span><a href="#(part._.Relaying_across_layers)" class="tocsubseclink" data-pltdoc="x">Relaying across layers</a></td></tr></table></div></div><div class="maincolumn"><div class="main"><div class="versionbox"><span class="version">5.3.4.10</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
|
|
the <span style="font-style: italic">C library interface</span> of a Unix-like operating system. The
|
|
<a href="low-level-interface.html" data-pltdoc="x">Low-level interface</a> corresponds to the <span style="font-style: italic">system call
|
|
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><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="#%28mod-path._marketplace%29" class="RktModLink" data-pltdoc="x"><span class="RktSym">marketplace</span></a></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"><span class="badlink"><span class="RktValLink">ground-vm:</span></span></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><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="#%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><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="#%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></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"><span class="badlink"><span class="RktValLink">ground-vm</span></span></span>/<span class="RktSym"><span class="badlink"><span class="RktValLink">ground-vm:</span></span></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"><span class="badlink"><span class="RktValLink">ground-vm</span></span></span> along with
|
|
<span class="RktSym"><span class="badlink"><span class="RktValLink">tcp</span></span></span> and an initial <span class="RktSym"><span class="badlink"><span class="RktValLink">endpoint</span></span></span> action:</p><blockquote class="SCodeFlow"><table cellspacing="0" class="RktBlk"><tr><td><span class="RktPn">(</span><span class="RktSym"><span class="badlink"><span class="RktValLink">ground-vm</span></span></span></td></tr><tr><td><span class="hspace"> </span><span class="RktSym"><span class="badlink"><span class="RktValLink">tcp</span></span></span></td></tr><tr><td><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><span class="badlink"><span class="RktValLink">endpoint</span></span></span><span class="hspace"> </span><span class="RktPn">#:subscriber</span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym">tcp-channel</span><span class="hspace"> </span><span class="RktSym"><span class="badlink"><span class="RktValLink">?</span></span></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"><span class="badlink"><span class="RktValLink">?</span></span></span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace"> </span><span class="RktPn">#:conversation</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">#:on-presence</span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><span class="badlink"><span class="RktValLink">spawn</span></span></span><span class="hspace"> </span><span class="RktPn">#:child</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></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"><span class="badlink"><span class="RktValLink">ground-vm</span></span></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-untyped..rkt)._ground-vm~3a))"></a><span title="Provided from: marketplace/sugar-untyped, marketplace/sugar-typed"><span class="RktSym"><span class="badlink"><span class="RktValLink">ground-vm:</span></span></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"><span class="badlink"><span class="RktValLink">ground-vm:</span></span></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><span class="RktSym"><span class="badlink"><span class="RktValLink">transition</span></span></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><span class="RktSym"><span class="badlink"><span class="RktValLink">transition:</span></span></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><span class="RktSym"><span class="badlink"><span class="RktValLink">transition/no-state</span></span></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"><span class="badlink"><span class="RktValLink">Transition</span></span></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"><span class="badlink"><span class="RktValLink">ActionTree</span></span></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"><span class="badlink"><span class="RktValLink">transition/no-state</span></span></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"><span class="badlink"><span class="RktValLink">transition/no-state</span></span></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><span class="RktSym"><span class="badlink"><span class="RktValLink">transition</span></span></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"><span class="badlink"><span class="RktValLink">ActionTree</span></span></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"><span class="RktSym"><span class="badlink"><span class="RktValLink">Transition</span></span></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"><span class="badlink"><span class="RktValLink">transition</span></span></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"><span class="badlink"><span class="RktValLink">transition-state</span></span></span> field is the new
|
|
private state the process will have after the transition is applied,
|
|
and the <span class="RktSym"><span class="badlink"><span class="RktValLink">transition-actions</span></span></span> are the actions that will be
|
|
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"><span class="RktSym"><span class="badlink"><span class="RktValLink">ActionTree</span></span></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"><span class="badlink"><span class="RktValLink">Constreeof</span></span></span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><span class="badlink"><span class="RktValLink">Action</span></span></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"><span class="RktSym"><span class="badlink"><span class="RktValLink">Constreeof</span></span></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"><span class="badlink"><span class="RktValLink">Action</span></span></span>s. When
|
|
performing actions, a VM will traverse an action-tree in left-to-right
|
|
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
|
|
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
|
|
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"><span class="badlink"><span class="RktValLink">send-message</span></span></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"><span class="badlink"><span class="RktValLink">send-message</span></span></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"><span class="badlink"><span class="RktValLink">send-message</span></span></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"><span class="badlink"><span class="RktValLink">send-message</span></span></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"><span class="badlink"><span class="RktValLink">send-message</span></span></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"><span class="badlink"><span class="RktValLink">send-message</span></span></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"><span class="badlink"><span class="RktValLink">send-message</span></span></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"><span class="badlink"><span class="RktValLink">send-message</span></span></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"><span class="badlink"><span class="RktValLink">send-message</span></span></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
|
|
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
|
|
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
|
|
at all" in a transition:</p><blockquote class="SCodeFlow"><table cellspacing="0" class="RktBlk"><tr><td><span class="RktPn">(</span><span class="RktSym"><span class="badlink"><span class="RktValLink">transition</span></span></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"><span class="badlink"><span class="RktValLink">transition</span></span></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"><span class="badlink"><span class="RktValLink">transition</span></span></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"><span class="badlink"><span class="RktValLink">transition</span></span></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><span class="RktSym"><span class="badlink"><span class="RktValLink">sequence-actions</span></span></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"><span class="badlink"><span class="RktValLink">Transition</span></span></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"><span class="badlink"><span class="RktValLink">Transition</span></span></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"><span class="badlink"><span class="RktValLink">ActionTree</span></span></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"><span class="badlink"><span class="RktValLink">Transition</span></span></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>
|
|
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"><span class="badlink"><span class="RktValLink">ActionTree</span></span></span>, it is appended to the pending transition’s
|
|
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
|
|
transition.</div></p><p>For example,</p><blockquote class="SCodeFlow"><table cellspacing="0" class="RktBlk"><tr><td><span class="RktPn">(</span><span class="RktSym"><span class="badlink"><span class="RktValLink">sequence-actions</span></span></span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><span class="badlink"><span class="RktValLink">transition</span></span></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"><span class="badlink"><span class="RktValLink">send-message</span></span></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"><span class="badlink"><span class="RktValLink">send-message</span></span></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"><span class="badlink"><span class="RktValLink">send-message</span></span></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"><span class="badlink"><span class="RktValLink">transition</span></span></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"><span class="badlink"><span class="RktValLink">send-message</span></span></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"><span class="badlink"><span class="RktValLink">send-message</span></span></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"><span class="badlink"><span class="RktValLink">transition</span></span></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"><span class="badlink"><span class="RktValLink">send-message</span></span></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"><span class="badlink"><span class="RktValLink">send-message</span></span></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"><span class="badlink"><span class="RktValLink">send-message</span></span></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"><span class="badlink"><span class="RktValLink">send-message</span></span></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"><span class="badlink"><span class="RktValLink">send-message</span></span></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
|
|
<span class="RktSym"><span class="badlink"><span class="RktValLink">add-endpoint</span></span></span>, but because endpoints are the most flexible and
|
|
complex point of interaction between a process and its VM, a DSL,
|
|
<span class="RktSym"><span class="badlink"><span class="RktValLink">endpoint</span></span></span>, streamlines 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><table cellspacing="0" class="RktBlk RForeground"><tr><td><span class="RktPn">(</span><span class="RktSym"><span class="badlink"><span class="RktValLink">endpoint</span></span></span><span class="hspace"> </span><span class="RktVar">orientation</span><span class="hspace"> </span><span class="RktVar">topic</span><span class="hspace"> </span><span class="RktVar">maybe-interest-type</span></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">maybe-let-name</span></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">maybe-name</span></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">maybe-state-pattern</span></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">maybe-on-presence</span></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">maybe-on-absence</span></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">maybe-role-patterns</span></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">maybe-reason-pattern</span></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">maybe-message-handlers</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><span class="RktSym"><span class="badlink"><span class="RktValLink">endpoint:</span></span></span><span class="hspace"> </span><span class="RktVar">maybe-typed-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></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">orientation</span><span class="hspace"> </span><span class="RktVar">topic</span><span class="hspace"> </span><span class="RktVar">maybe-interest-type</span></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">maybe-let-name</span></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">maybe-name</span></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">maybe-on-presence</span></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">maybe-on-absence</span></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">maybe-role-patterns</span></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">maybe-reason-pattern</span></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">maybe-message-handlers</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-typed-state-pattern</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="RktVar">pattern</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">orientation</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">#:subscriber</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">|</td><td align="left" valign="baseline"><span class="stt"> </span></td><td align="left" valign="baseline"><span class="RktPn">#:publisher</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">topic</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">maybe-interest-type</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">#:participant</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">|</td><td align="left" valign="baseline"><span class="stt"> </span></td><td align="left" valign="baseline"><span class="RktPn">#:observer</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">|</td><td align="left" valign="baseline"><span class="stt"> </span></td><td align="left" valign="baseline"><span class="RktPn">#:everything</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-let-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">#:let-name</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-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">#: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">maybe-state-pattern</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">#:state</span><span class="hspace"> </span><span class="RktVar">pattern</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-on-presence</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">#:on-presence</span><span class="hspace"> </span><span class="RktVar">handler-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-on-absence</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">#:on-absence</span><span class="hspace"> </span><span class="RktVar">handler-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-role-patterns</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">#:role</span><span class="hspace"> </span><span class="RktVar">pattern</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">|</td><td align="left" valign="baseline"><span class="stt"> </span></td><td align="left" valign="baseline"><table cellspacing="0" class="RktBlk"><tr><td><span class="RktPn">#:peer-orientation</span><span class="hspace"> </span><span class="RktVar">pattern</span></td></tr><tr><td><span class="RktPn">#:conversation</span><span class="hspace"> </span><span class="RktVar">pattern</span></td></tr><tr><td><span class="RktPn">#:peer-interest-type</span><span class="hspace"> </span><span class="RktVar">pattern</span></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"><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-reason-pattern</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">#:reason</span><span class="hspace"> </span><span class="RktVar">pattern</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-message-handlers</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="RktVar">message-handler</span><span class="hspace"> </span><span class="RktMeta">...</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">message-handler</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">[</span><span class="RktVar">pattern</span><span class="hspace"> </span><span class="RktVar">handler-expr</span><span class="RktPn">]</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">handler-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">Almost everything is optional in an <span class="RktSym"><span class="badlink"><span class="RktValLink">endpoint</span></span></span>. The only
|
|
mandatory parts are the orientation and the topic. For
|
|
<span class="RktSym"><span class="badlink"><span class="RktValLink">endpoint:</span></span></span>, the expected type of the process state must also
|
|
be supplied.</div></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"><span class="badlink"><span class="RktValLink">endpoint</span></span></span><span class="hspace"> </span><span class="RktPn">#:subscriber</span><span class="hspace"> </span><span class="RktSym"><span class="badlink"><span class="RktValLink">?</span></span></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
|
|
state type,</p><blockquote class="SCodeFlow"><p><span class="RktPn">(</span><span class="RktSym"><span class="badlink"><span class="RktValLink">endpoint:</span></span></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="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="RktPn">#:subscriber</span><span class="hspace"> </span><span class="RktSym"><span class="badlink"><span class="RktValLink">?</span></span></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"><span class="badlink"><span class="RktValLink">endpoint</span></span></span><span class="hspace"> </span><span class="RktPn">#:publisher</span><span class="hspace"> </span><span class="RktSym"><span class="badlink"><span class="RktValLink">?</span></span></span><span class="RktPn">)</span></td></tr><tr><td><span class="RktPn">(</span><span class="RktSym"><span class="badlink"><span class="RktValLink">endpoint:</span></span></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="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="RktPn">#:publisher</span><span class="hspace"> </span><span class="RktSym"><span class="badlink"><span class="RktValLink">?</span></span></span><span class="RktPn">)</span></td></tr></table></blockquote><p>While topic patterns are ordinary Racket data with embedded <span class="RktSym"><span class="badlink"><span class="RktValLink">?</span></span></span>
|
|
wildcards (see <a href="Concepts.html#%28part._messages-and-topics%29" data-pltdoc="x">Messages and Topics</a>), all the other patterns
|
|
in an <span class="RktSym"><span class="badlink"><span class="RktValLink">endpoint</span></span></span> are <span class="RktSym">match</span>-patterns. In particular
|
|
note that <span class="RktSym"><span class="badlink"><span class="RktValLink">?</span></span></span> is a wildcard in a topic pattern, while
|
|
<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>Supply one or more <span class="RktVar">message-handler</span> clauses to handle incoming
|
|
message events (as distinct from presence- or absence-events).</p><p>The following endpoint <span style="font-style: italic">subscribes</span> to all messages, but only
|
|
<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"><span class="badlink"><span class="RktValLink">endpoint</span></span></span><span class="hspace"> </span><span class="RktPn">#:subscriber</span><span class="hspace"> </span><span class="RktSym"><span class="badlink"><span class="RktValLink">?</span></span></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"><span class="badlink"><span class="RktValLink">send-message</span></span></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"><span class="badlink"><span class="RktValLink">send-message</span></span></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"><span class="badlink"><span class="RktValLink">quit</span></span></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>If <span class="RktPn">#:state</span> occurs in an <span class="RktSym"><span class="badlink"><span class="RktValLink">endpoint</span></span></span>, or the
|
|
<span class="RktVar">maybe-typed-state-pattern</span> occurs in an <span class="RktSym"><span class="badlink"><span class="RktValLink">endpoint:</span></span></span>,
|
|
then all the <span class="RktVar">handler-expr</span>s in that endpoint are expected to
|
|
return <a href="#%28part._constructing-transitions%29" data-pltdoc="x">transition structures</a>.</p><p>If not, however, the event handler expressions are expected to return
|
|
plain <span class="RktSym"><span class="badlink"><span class="RktValLink">ActionTree</span></span></span>s.</p><p>This way, simple endpoints that do not need to examine the process
|
|
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"><span class="badlink"><span class="RktValLink">endpoint</span></span></span><span class="hspace"> </span><span class="RktPn">#:subscriber</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="RktVal">'</span><span class="RktVal">ping</span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><span class="badlink"><span class="RktValLink">send-message</span></span></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></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"><span class="badlink"><span class="RktValLink">endpoint</span></span></span><span class="hspace"> </span><span class="RktPn">#:subscriber</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">#:state</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="RktVal">'</span><span class="RktVal">ping</span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><span class="badlink"><span class="RktValLink">transition</span></span></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"><span class="badlink"><span class="RktValLink">send-message</span></span></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><h5>2.4.3<tt> </tt><a name="(part._naming-endpoints)"></a>Naming endpoints</h5><p>Endpoint names can be used to <a href="#%28part._updating-endpoints%29" data-pltdoc="x">update</a>
|
|
or <a href="#%28part._deleting-endpoints%29" data-pltdoc="x">delete</a> endpoints.</p><p>If <span class="RktPn">#:name</span> is supplied, the given value is used as the name of
|
|
the endpoint. If not, a fresh name is created. (At present,
|
|
<span class="RktSym"><a href="http://docs.racket-lang.org/reference/symbols.html#%28def._%28%28quote._~23~25kernel%29._gensym%29%29" class="RktValLink" data-pltdoc="x">gensym</a></span> is used.)</p><p>If <span class="RktPn">#:let-name</span> is supplied, the given identifier is bound in
|
|
the <span class="RktVar">handler-expr</span>s to the name of the endpoint. If not, the
|
|
name of the endpoint is inaccessible to the <span class="RktVar">handler-expr</span>s.</p><h5>2.4.4<tt> </tt><a name="(part._.Handling_presence_and_absence_events)"></a>Handling presence and absence events</h5><p>Other endpoints (in this or other processes) may have matching topics
|
|
and complementary orientations to the current endpoint. When such
|
|
endpoints come and go, presence and absence events are generated in
|
|
the current endpoint.</p><p>By default, no actions are taken on such events, but
|
|
<span class="RktPn">#:on-presence</span> and <span class="RktPn">#:on-absence</span> override this
|
|
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"><span class="badlink"><span class="RktValLink">endpoint</span></span></span><span class="hspace"> </span><span class="RktPn">#:subscriber</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">#:on-presence</span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><span class="badlink"><span class="RktValLink">send-message</span></span></span><span class="hspace"> </span><span class="RktVal">'</span><span class="RktVal">pinger-arrived</span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace"> </span><span class="RktPn">#:on-absence</span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><span class="badlink"><span class="RktValLink">send-message</span></span></span><span class="hspace"> </span><span class="RktVal">'</span><span class="RktVal">pinger-departed</span><span class="RktPn">)</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"><span class="badlink"><span class="RktValLink">send-message</span></span></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></td></tr></table></blockquote><p>Some time later, process B takes the following endpoint-establishing
|
|
action:</p><blockquote class="SCodeFlow"><table cellspacing="0" class="RktBlk"><tr><td><span class="RktPn">(</span><span class="RktSym"><span class="badlink"><span class="RktValLink">endpoint</span></span></span><span class="hspace"> </span><span class="RktPn">#:publisher</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">#:let-name</span><span class="hspace"> </span><span class="RktSym">ping-endpoint-name</span></td></tr><tr><td><span class="hspace"> </span><span class="RktPn">#:on-presence</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"><span class="badlink"><span class="RktValLink">endpoint</span></span></span><span class="hspace"> </span><span class="RktPn">#:subscriber</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">#:let-name</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="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"><span class="badlink"><span class="RktValLink">delete-endpoint</span></span></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"><span class="badlink"><span class="RktValLink">delete-endpoint</span></span></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></td></tr><tr><td><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><span class="badlink"><span class="RktValLink">send-message</span></span></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></td></tr></table></blockquote><p>The sequence of events will be:</p><ol><li><p>Process A’s <span class="RktPn">#:on-presence</span> handler will run, and the
|
|
<span class="RktVal">'</span><span class="RktVal">pinger-arrived</span> message will be sent. At the same
|
|
time,<span class="NoteBox"><span class="NoteContent">In the current implementation, one happens before the
|
|
other, but it is nondeterministic which is run first.</span></span> process B’s
|
|
<span class="RktPn">#:on-presence</span> handler runs, installing a second endpoint
|
|
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
|
|
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>
|
|
message, and deletes both of process B’s endpoints.</p></li><li><p>The <span class="RktPn">#:on-absence</span> handler in process A runs, sending
|
|
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
|
|
<span class="RktPn">#:on-presence</span> handler has fired, process B ensures that
|
|
someone is listening for pings.</p><p>This way, if process B starts before process A, then B will
|
|
automatically wait until A is ready to receive ping requests before
|
|
issuing any.</p><h5>2.4.5<tt> </tt><a name="(part._.Exit_reasons)"></a>Exit reasons</h5><p>If a <span class="RktPn">#:reason</span> pattern is supplied, then the exit reason
|
|
supplied to the <span class="RktSym"><span class="badlink"><span class="RktValLink">delete-endpoint</span></span></span> or <span class="RktSym"><span class="badlink"><span class="RktValLink">quit</span></span></span> action that
|
|
led to the <span class="RktSym"><span class="badlink"><span class="RktValLink">absence-event</span></span></span> is available to the endpoint’s
|
|
<span class="RktPn">#:on-absence</span> handler expression.</p><h5>2.4.6<tt> </tt><a name="(part._updating-endpoints)"></a>Updating endpoints</h5><p>If, when an endpoint is created, an existing endpoint with an
|
|
<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
|
|
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
|
|
signals. A future release of this library will include better
|
|
automatic support for avoiding such transients.</p><h5>2.4.7<tt> </tt><a name="(part._.Who_am_.I_talking_to_)"></a>Who am I talking to?</h5><p>If either <span class="RktPn">#:role</span> or any of <span class="RktPn">#:peer-orientation</span>,
|
|
<span class="RktPn">#:conversation</span>, or <span class="RktPn">#:peer-interest-type</span> are
|
|
supplied, the <span class="RktVar">handler-expr</span>s are given access to the role
|
|
carried in the <span class="RktSym"><span class="badlink"><span class="RktValLink">EndpointEvent</span></span></span> that triggered them.</p><p>This role describes the <span style="font-style: italic">intersection of interests</span> 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>Using <span class="RktPn">#:role</span> allows a handler complete access to the
|
|
<span class="RktSym"><span class="badlink"><span class="RktValLink">role</span></span></span> structure in the triggering event. It is more common
|
|
however to simply use <span class="RktPn">#:conversation</span> to extract the
|
|
<span class="RktSym"><span class="badlink"><span class="RktValLink">role-topic</span></span></span> alone, since it is seldom necessary to examine
|
|
<span class="RktSym"><span class="badlink"><span class="RktValLink">role-orientation</span></span></span> (since it’s guaranteed to be complementary
|
|
to the orientation of the current endpoint) or
|
|
<span class="RktSym"><span class="badlink"><span class="RktValLink">role-interest-type</span></span></span>. If access to those parts is required, use
|
|
<span class="RktPn">#:peer-orientation</span> and <span class="RktPn">#:peer-interest-type</span>.</p><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><span class="RktSym"><span class="badlink"><span class="RktValLink">delete-endpoint</span></span></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"><span class="badlink"><span class="RktValLink">Action</span></span></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="RktSym">delete-endpoint-id</span> 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"><span class="badlink"><span class="RktValLink">add-endpoint-pre-eid</span></span></span>; when <span class="RktSym"><span class="badlink"><span class="RktValLink">endpoint</span></span></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="#%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"><span class="badlink"><span class="RktValLink">absence-event</span></span></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><span class="RktSym"><span class="badlink"><span class="RktValLink">send-message</span></span></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"><span class="badlink"><span class="RktValLink">Action</span></span></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"><span class="badlink"><span class="RktValLink">Orientation</span></span></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><span class="RktSym"><span class="badlink"><span class="RktValLink">send-feedback</span></span></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"><span class="badlink"><span class="RktValLink">Action</span></span></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"><span class="badlink"><span class="RktValLink">send-message</span></span></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><table cellspacing="0" class="RktBlk RForeground"><tr><td><span class="RktPn">(</span><span class="RktSym"><span class="badlink"><span class="RktValLink">spawn</span></span></span><span class="hspace"> </span><span class="RktVar">maybe-pid-binding</span><span class="hspace"> </span><span class="RktVar">maybe-debug-name</span><span class="hspace"> </span><span class="RktVar">maybe-parent-continuation</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><span class="RktSym"><span class="badlink"><span class="RktValLink">spawn:</span></span></span><span class="hspace"> </span><span class="RktVar">maybe-pid-binding</span><span class="hspace"> </span><span class="RktVar">maybe-debug-name</span><span class="hspace"> </span><span class="RktVar">typed-parent-continuation</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">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">maybe-parent-continuation</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">#:parent</span><span class="hspace"> </span><span class="RktVar">k-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">|</td><td align="left" valign="baseline"><span class="stt"> </span></td><td align="left" valign="baseline"><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 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">typed-parent-continuation</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">#: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 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">#: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><span class="hspace"> </span><span class="RktVar">k-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">|</td><td align="left" valign="baseline"><span class="stt"> </span></td><td align="left" valign="baseline"><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 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>
|
|
should be an expression yielding a <span class="RktSym"><span class="badlink"><span class="RktValLink">transition</span></span></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>Any supplied <span class="RktPn">#:debug-name</span> will be used in VM debug output.
|
|
See also <a href="Management_and_Monitoring.html#%28part._logging%29" data-pltdoc="x">logging (MATRIX_LOG)</a>.</p><p>If <span class="RktPn">#:parent</span> is supplied, the associated <span class="RktVar">k-expr</span> will
|
|
run in the parent process after the child process has been created. If
|
|
the <span class="RktVar">parent-state-pattern</span> is also supplied, then
|
|
<span class="RktVar">k-expr</span> must return a <span class="RktSym"><span class="badlink"><span class="RktValLink">Transition</span></span></span>; otherwise, it must
|
|
return an <span class="RktSym"><span class="badlink"><span class="RktValLink">ActionTree</span></span></span>. Note that in Typed Racket, for type
|
|
system reasons, <span class="RktSym"><span class="badlink"><span class="RktValLink">spawn:</span></span></span> requires <span class="RktVar">ParentStateType</span> to
|
|
be supplied.</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><span class="RktSym"><span class="badlink"><span class="RktValLink">quit</span></span></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"><span class="badlink"><span class="RktValLink">Action</span></span></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"><span class="badlink"><span class="RktValLink">PID</span></span></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
|
|
omitted or <span class="RktVal">#f</span>, terminates the acting process; otherwise,
|
|
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
|
|
action, and made available in any resulting <span class="RktSym"><span class="badlink"><span class="RktValLink">absence-event</span></span></span>s.</p><p>Terminating the current process is as simple as:</p><blockquote class="SCodeFlow"><p><span class="RktPn">(</span><span class="RktSym"><span class="badlink"><span class="RktValLink">quit</span></span></span><span class="RktPn">)</span></p></blockquote><p>When a process raises an exception that it does not catch, its
|
|
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
|
|
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><span class="RktSym"><span class="badlink"><span class="RktValLink">yield</span></span></span><span class="hspace"> </span><span class="RktVar">maybe-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><span class="RktSym"><span class="badlink"><span class="RktValLink">yield:</span></span></span><span class="hspace"> </span><span class="RktVar">typed-state-pattern</span><span class="hspace"> </span><span class="RktVar">k-expr</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-state-pattern</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">#:state</span><span class="hspace"> </span><span class="RktVar">pattern</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">typed-state-pattern</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="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></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="RktVar">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></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></table></td></tr></table></td></tr></table></blockquote></div><div class="SIntrapara">Lets other processes in the system run for a step, returning to
|
|
evaluate <span class="RktVar">k-expr</span> only after doing a complete round of the
|
|
scheduler.</div></p><p>If <span class="RktVar">pattern</span> is supplied, <span class="RktVar">k-expr</span> should evaluate to a
|
|
<span class="RktSym"><span class="badlink"><span class="RktValLink">Transition</span></span></span>; otherwise it should produce an <span class="RktSym"><span class="badlink"><span class="RktValLink">ActionTree</span></span></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><span class="RktSym"><span class="badlink"><span class="RktValLink">nested-vm</span></span></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><span class="RktSym"><span class="badlink"><span class="RktValLink">nested-vm:</span></span></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"><span class="badlink"><span class="RktValLink">spawn</span></span></span> action that starts a nested VM. The
|
|
primordial process in the new VM executes the boot-actions with the
|
|
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>
|
|
is used.)</div></p><p>If <span class="RktPn">#:vm-pid</span> is present, the corresponding identifier is bound
|
|
in the boot-action expressions to the container-relative PID of the
|
|
new VM itself. If <span class="RktPn">#:boot-pid</span> is present, however, the
|
|
corresponding identifier is bound to the new-VM-relative PID of the
|
|
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><span class="RktSym"><span class="badlink"><span class="RktValLink">at-meta-level:</span></span></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><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><span class="RktSym"><span class="badlink"><span class="RktValLink">at-meta-level</span></span></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"><span class="badlink"><span class="RktValLink">Action</span></span></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"><span class="badlink"><span class="RktValLink">PreAction</span></span></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
|
|
<span style="font-style: italic">internal</span> one, provided for the VM’s processes to talk amongst
|
|
themselves, and the <span style="font-style: italic">external</span> one, the network that the VM
|
|
itself is a process within.</div></p><p>Marketplace’s actions can apply to either of those two networks. By
|
|
default, actions apply to the VM of the acting process directly, but
|
|
using <span class="RktSym"><span class="badlink"><span class="RktValLink">at-meta-level</span></span></span> (or <span class="RktSym"><span class="badlink"><span class="RktValLink">at-meta-level:</span></span></span> in typed
|
|
code) to wrap an action <span style="font-style: italic">level-shifts</span> the action to make it
|
|
apply at the level of the acting process’s VM’s container instead.</p><p>For example, wrapping an <span class="RktSym"><span class="badlink"><span class="RktValLink">endpoint</span></span></span> in <span class="RktSym"><span class="badlink"><span class="RktValLink">at-meta-level</span></span></span>
|
|
adds a subscription to the VM’s container’s network. Instead of
|
|
listening to sibling processes of the acting process, the new endpoint
|
|
will listen to sibling processes of the acting process’s VM. In this
|
|
example, the primordial process in the <span class="RktSym"><span class="badlink"><span class="RktValLink">nested-vm</span></span></span> creates an
|
|
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"><span class="badlink"><span class="RktValLink">nested-vm</span></span></span></td></tr><tr><td><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><span class="badlink"><span class="RktValLink">at-meta-level</span></span></span></td></tr><tr><td><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><span class="badlink"><span class="RktValLink">endpoint</span></span></span><span class="hspace"> </span><span class="RktPn">#:subscriber</span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym">tcp-channel</span><span class="hspace"> </span><span class="RktSym"><span class="badlink"><span class="RktValLink">?</span></span></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"><span class="badlink"><span class="RktValLink">?</span></span></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
|
|
<span class="RktSym"><span class="badlink"><span class="RktValLink">nested-vm</span></span></span> 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"><span class="badlink"><span class="RktValLink">nested-vm</span></span></span></td></tr><tr><td><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><span class="badlink"><span class="RktValLink">at-meta-level</span></span></span></td></tr><tr><td><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><span class="badlink"><span class="RktValLink">spawn</span></span></span><span class="hspace"> </span><span class="RktPn">#:child</span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><span class="badlink"><span class="RktValLink">transition/no-state</span></span></span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><span class="badlink"><span class="RktValLink">send-message</span></span></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
|
|
<span class="RktSym"><span class="badlink"><span class="RktValLink">nested-vm</span></span></span>’s primordial process:</p><blockquote class="SCodeFlow"><table cellspacing="0" class="RktBlk"><tr><td><span class="RktPn">(</span><span class="RktSym"><span class="badlink"><span class="RktValLink">nested-vm</span></span></span></td></tr><tr><td><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><span class="badlink"><span class="RktValLink">spawn</span></span></span><span class="hspace"> </span><span class="RktPn">#:child</span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><span class="badlink"><span class="RktValLink">transition/no-state</span></span></span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><span class="badlink"><span class="RktValLink">send-message</span></span></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> |