containing <ahref="Concepts.html#%28tech._vm%29"class="techoutside"data-pltdoc="x"><spanclass="techinside">VM</span></a> is based on <ahref="#%28tech._handler._function%29"class="techoutside"data-pltdoc="x"><spanclass="techinside">handler functions</span></a> exchanging
<ahref="Concepts.html#%28tech._event%29"class="techoutside"data-pltdoc="x"><spanclass="techinside">event</span></a> and <ahref="Concepts.html#%28tech._action%29"class="techoutside"data-pltdoc="x"><spanclass="techinside">action</span></a> structures with the VM. Both events and
actions are simple Racket structures.</p><p>This low-level interface between a VM and a process is analogous to
the <spanstyle="font-style: italic">system call interface</span> of a Unix-like operating system. The
<ahref="high-level-interface.html"data-pltdoc="x">High-level interface</a> corresponds to the <spanstyle="font-style: italic">C library
interface</span> of a Unix-like operating system.</p><h4>3.1<tt> </tt><aname="(part._handler-functions)"></a>Handler Functions</h4><p>Each <aname="(tech._handler._function)"></a><spanstyle="font-style: italic">handler function</span> is always associated with a particular
<ahref="Concepts.html#%28tech._endpoint%29"class="techoutside"data-pltdoc="x"><spanclass="techinside">endpoint</span></a>, registered with the VM via
<spanclass="RktSym"><ahref="high-level-interface.html#%28form._%28%28lib._marketplace%2Fsugar-untyped..rkt%29._endpoint%29%29"class="RktStxLink"data-pltdoc="x">endpoint</a></span>/<spanclass="RktSym"><ahref="high-level-interface.html#%28form._%28%28lib._marketplace%2Fsugar-typed..rkt%29._endpoint~3a%29%29"class="RktStxLink"data-pltdoc="x">endpoint:</a></span>/<spanclass="RktSym"><ahref="#%28def._%28%28lib._marketplace%2Fmain..rkt%29._add-endpoint%29%29"class="RktValLink"data-pltdoc="x">add-endpoint</a></span>. A handler
function for a given process with state type <spanclass="RktSym">State</span> has type:</p><blockquoteclass="SCodeFlow"><p><spanclass="RktPn">(</span><spanclass="RktSym"><ahref="#%28def._%28%28lib._marketplace%2Fmain..rkt%29._.Endpoint.Event%29%29"class="RktValLink"data-pltdoc="x">EndpointEvent</a></span><spanclass="hspace"> </span><spanclass="RktSym"><ahref="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"><spanclass="nobreak">-></span></a></span><spanclass="hspace"> </span><spanclass="RktSym">State</span><spanclass="hspace"> </span><spanclass="RktSym"><ahref="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"><spanclass="nobreak">-></span></a></span><spanclass="hspace"> </span><spanclass="RktPn">(</span><spanclass="RktSym"><ahref="high-level-interface.html#%28def._%28%28lib._marketplace%2Fmain..rkt%29._.Transition%29%29"class="RktValLink"data-pltdoc="x">Transition</a></span><spanclass="hspace"> </span><spanclass="RktSym">State</span><spanclass="RktPn">)</span><spanclass="RktPn">)</span></p></blockquote><p>That is, given an <spanclass="RktSym"><ahref="#%28def._%28%28lib._marketplace%2Fmain..rkt%29._.Endpoint.Event%29%29"class="RktValLink"data-pltdoc="x">EndpointEvent</a></span> followed by the process’s
current state, the handler should reply with a <spanclass="RktSym"><ahref="high-level-interface.html#%28def._%28%28lib._marketplace%2Fmain..rkt%29._.Transition%29%29"class="RktValLink"data-pltdoc="x">Transition</a></span>
containing a new process state and a collection of <spanclass="RktSym"><ahref="#%28def._%28%28lib._marketplace%2Fmain..rkt%29._.Action%29%29"class="RktValLink"data-pltdoc="x">Action</a></span>s.</p><p><divclass="SIntrapara"><blockquoteclass="SVInsetFlow"><tablecellspacing="0"class="boxed RBoxed"><tr><td><tablecellspacing="0"class="together"><tr><td><blockquoteclass="SubFlow"><divclass="RBackgroundLabel SIEHidden"><divclass="RBackgroundLabelInner"><p>type</p></div></div><pclass="RForeground"><aname="(def._((lib._marketplace/main..rkt)._.Handler))"></a><spantitle="Provided from: marketplace"><spanclass="RktSym"><ahref="#%28def._%28%28lib._marketplace%2Fmain..rkt%29._.Handler%29%29"class="RktValLink"data-pltdoc="x">Handler</a></span></span><spanclass="hspace"> </span>:<spanclass="hspace"> </span><spanclass="RktPn">(</span><spanclass="RktSym"><ahref="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><spanclass="hspace"> </span><spanclass="RktPn">(</span><spanclass="RktSym">State</span><spanclass="RktPn">)</span><spanclass="hspace"> </span><spanclass="RktPn">(</span><spanclass="RktSym"><ahref="#%28def._%28%28lib._marketplace%2Fmain..rkt%29._.Trap.K%29%29"class="RktValLink"data-pltdoc="x">TrapK</a></span><spanclass="hspace"> </span><spanclass="RktSym">State</span><spanclass="RktPn">)</span><spanclass="RktPn">)</span></p></blockquote></td></tr></table></td></tr><tr><td><tablecellspacing="0"class="together"><tr><td><blockquoteclass="SubFlow"><divclass="RBackgroundLabel SIEHidden"><divclass="RBackgroundLabelInner"><p>type</p></div></div><pclass="RForeground"><aname="(def._((lib._marketplace/main..rkt)._.Trap.K))"></a><spantitle="Provided from: marketplace"><spanclass="RktSym"><ahref="#%28def._%28%28lib._marketplace%2Fmain..rkt%29._.Trap.K%29%29"class="RktValLink"data-pltdoc="x">TrapK</a></span></span><spanclass="hspace"> </span>:<spanclass="hspace"> </span><spanclass="RktPn">(</span><spanclass="RktSym"><ahref="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><spanclass="hspace"> </span><spanclass="RktPn">(</span><spanclass="RktSym">State</span><spanclass="RktPn">)</span><spanclass="hspace"> </span><spanclass="RktPn">(</span><spanclass="RktSym"><ahref="#%28def._%28%28lib._marketplace%2Fmain..rkt%29._.Endpoint.Event%29%29"class="RktValLink"data-pltdoc="x">EndpointEvent</a></span><spanclass="hspace"> </span><spanclass="RktSym"><ahref="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"><spanclass="nobreak">-></span></a></span><spanclass="hspace"> </span><spanclass="RktPn">(</span><spanclass="RktSym"><ahref="#%28def._%28%28lib._marketplace%2Fmain..rkt%29._.Interrupt.K%29%29"class="RktValLink"data-pltdoc="x">InterruptK</a></span><spanclass="hspace"> </span><spanclass="RktSym">State</span><spanclass="RktPn">)</span><spanclass="RktPn">)</span><spanclass="RktPn">)</span></p></blockquote></td></tr></table></td></tr><tr><td><tablecellspacing="0"class="together"><tr><td><blockquoteclass="SubFlow"><divclass="RBackgroundLabel SIEHidden"><divclass="RBackgroundLabelInner"><p>type</p></div></div><pclass="RForeground"><aname="(def._((lib._marketplace/main..rkt)._.Interrupt.K))"></a><spantitle="Provided from: marketplace"><spanclass="RktSym"><ahref="#%28def._%28%28lib._marketplace%2Fmain..rkt%29._.Interrupt.K%29%29"class="RktValLink"data-pltdoc="x">InterruptK</a></span></span><spanclass="hspace"> </span>:<spanclass="hspace"> </span><spanclass="RktPn">(</span><spanclass="RktSym"><ahref="http://docs.racket-lang.org/ts-reference/type-ref.html#%28form._%28%28lib._typed-racket%2Fbase-env%2Fba
and <ahref="Concepts.html#%28tech._topic%29"class="techoutside"data-pltdoc="x"><spanclass="techinside">topics</span></a> are ordinary Racket values which may have embedded
wildcards.</div></p><p><divclass="SIntrapara"><blockquoteclass="SVInsetFlow"><tablecellspacing="0"class="boxed RBoxed"><tr><td><tablecellspacing="0"class="together"><tr><td><blockquoteclass="SubFlow"><divclass="RBackgroundLabel SIEHidden"><divclass="RBackgroundLabelInner"><p>procedure</p></div></div><pclass="RForeground"><spanclass="RktPn">(</span><aname="(def._((lib._marketplace/main..rkt)._wild))"></a><spantitle="Provided from: marketplace, marketplace/sugar-untyped, marketplace/sugar-typed"><spanclass="RktSym"><ahref="#%28def._%28%28lib._marketplace%2Fmain..rkt%29._wild%29%29"class="RktValLink"data-pltdoc="x">wild</a></span></span><spanclass="RktPn"></span><spanclass="RktPn">)</span><spanclass="hspace"> </span>→<spanclass="hspace"> </span><spanclass="RktSym"><ahref="#%28def._%28%28lib._marketplace%2Fmain..rkt%29._.Topic%29%29"class="RktValLink"data-pltdoc="x">Topic</a></span></p></blockquote></td></tr></table></td></tr><tr><td><tablecellspacing="0"class="together"><tr><td><blockquoteclass="SubFlow"><divclass="RBackgroundLabel SIEHidden"><divclass="RBackgroundLabelInner"><p>syntax</p></div></div><pclass="RForeground"><aname="(def._((lib._marketplace/sugar-untyped..rkt)._~3f))"></a><spantitle="Provided from: marketplace, marketplace/sugar-untyped, marketplace/sugar-typed"><spanclass="RktSym"><ahref="#%28def._%28%28lib._marketplace%2Fsugar-untyped..rkt%29._~3f%29%29"class="RktValLink"data-pltdoc="x">?</a></span></span><spanclass="hspace"> </span>:<spanclass="hspace"> </span><spanclass="RktSym"><ahref="#%28def._%28%28lib._marketplace%2Fmain..rkt%29._.Topic%29%29"class="RktValLink"data-pltdoc="x">Topic</a></span></p></blockquote></td></tr></table></td></tr></table></blockquote></div><divclass="SIntrapara">Each time <spanclass="RktSym"><ahref="#%28def._%28%28lib._marketplace%2Fsugar-untyped..rkt%29._~3f%29%29"class="RktValLink"data-pltdoc="x">?</a></span> (or <spanclass="RktPn">(</span><spanclass="RktSym"><ahref="#%28def._%28%28lib._marketplace%2Fmain..rkt%29._wild%29%29"class="RktValLink"data-pltdoc="x">wild</a></span><spanclass="RktPn">)</span>) is used in an expression
context, it produces a fresh topic wildcard, suitable for use in a
topic pattern.</div></p><p><divclass="SIntrapara"><blockquoteclass="SVInsetFlow"><tablecellspacing="0"class="boxed RBoxed"><tr><td><tablecellspacing="0"class="together"><tr><td><blockquoteclass="SubFlow"><divclass="RBackgroundLabel SIEHidden"><divclass="RBackgroundLabelInner"><p>struct</p></div></div><tablecellspacing="0"class="RForeground"><tr><td><spanclass="RktPn">(</span><spanclass="RktSym"><ahref="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><spanclass="hspace"> </span></td><td><aname="(def._((lib._marketplace/main..rkt)._role-interest-type))"></a><aname="(def._((lib._marketplace/main..rkt)._role-topic))"></a><aname="(def._((lib._marketplace/main..rkt)._role-orientation))"></a><aname="(def._((lib._marketplace/main..rkt)._role~3f))"></a><aname="(def._((lib._marketplace/main..rkt)._struct~3arole))"></a><aname="(def._((lib._marketplace/main..rkt)._role))"></a><spantitle="Provided from: marketplace, marketplace/sugar-untyped, marketplace/sugar-typed"><spanclass="RktSym"><ahref="#%28def._%28%28lib._marketplace%2Fmain..rkt%29._role%29%29"class="RktValLink"data-pltdoc="x">role</a></span></span><spanclass="hspace"> </span><spanclass="RktPn">(</span><spanclass="RktSym">orientation</span><spanclass="stt"></span><spanclass="RktSym">topic</span><spanclass="stt"></span><spanclass="RktSym">interest-type</span><spanclass="RktPn">)</span></td></tr><tr><td><spanclass="hspace"> </span></td><td><spanclass="hspace"> </span></td><td><spanclass="RktPn">#:prefab</span><spanclass="RktPn">)</span></td></tr></table></blockquote></td></tr><tr><td><spanclass="hspace"> </span><spanclass="RktSym">orientation</span><spanclass="hspace"> </span>:<spanclass="hspace"> </span><spanclass="RktSym"><ahref="#%28def._%28%28lib._marketplace%2Fmain..rkt%29._.Orientation%29%29"class="RktValLink"data-pltdoc="x">Orientation</a></span></td></tr><tr><td><spanclass="hspace"> </span><spanclass="RktSym">topic</span><spanclass="hspace"> </span>:<spanclass="hspace"> </span><spanclass="RktSym"><ahref="#%28def._%28%28lib._marketplace%2Fmain..rkt%29._.Topic%29%29"class="RktValLink"data-pltdoc="x">Topic</a></span></td></tr><tr><td><spanclass="hspace"> </span><spanclass="RktSym">interest-type</span><spanclass="hspace"> </span>:<spanclass="hspace"> </span><spanclass="RktSym"><ahref="#%28def._%28%28lib._marketplace%2Fmain..rkt%29._.Interest.Type%29%29"class="RktValLink"data-pltdoc="x">InterestType</a></span></td></tr></table></td></tr><tr><td><tablecellspacing="0"class="together"><tr><td><blockquoteclass="SubFlow"><divclass="RBackgroundLabel SIEHidden"><divclass="RBackgroundLabelInner"><p>type</p></div></div><pclass="RForeground"><aname="(def._((lib._marketplace/main..rkt)._.Role))"></a><spantitle="Provided from: marketplace, marketplace/sugar-untyped, marketplace/sugar-typed"><spanclass="RktSym"><ahref="#%28def._%28%28lib._marketplace%2Fmain..rkt%29._.Role%29%29"class="RktValLink"data-pltdoc="x">Role</a></span></span><spanclass="hspace"> </span>:<spanclass="hspace"> </span><spanclass="RktSym"><ahref="#%28def._%28%28lib._marketplace%2Fmain..rkt%29._role%29%29"class="RktValLink"data-pltdoc="x">role</a></span></p></blockquote></td></tr></table></td></tr></table></blockquote></div><divclass="SIntrapara">Roles are almost always constructed by the
<spanclass="RktSym"><ahref="high-level-interface.html#%28form._%28%28lib._marketplace%2Fsugar-untyped..rkt%29._endpoint%29%29"class="RktStxLink"data-pltdoc="x">endpoint</a></span>/<spanclass="RktSym"><ahref="high-level-interface.html#%28form._%28%28lib._marketplace%2Fsugar-typed..rkt%29._endpoint~3a%29%29"class="RktStxLink"data-pltdoc="x">endpoint:</a></span> macros or by the VM
destructure <spanclass="RktSym"><ahref="#%28def._%28%28lib._marketplace%2Fmain..rkt%29._role%29%29"class="RktValLink"data-pltdoc="x">role</a></span> instances.</div></p><p>A <spanclass="RktSym"><ahref="#%28def._%28%28lib._marketplace%2Fmain..rkt%29._role%29%29"class="RktValLink"data-pltdoc="x">role</a></span> describes the conversational role of a peer as seen by
notification carrying the role</p><blockquoteclass="SCodeFlow"><p><spanclass="RktPn">(</span><spanclass="RktSym"><ahref="#%28def._%28%28lib._marketplace%2Fmain..rkt%29._role%29%29"class="RktValLink"data-pltdoc="x">role</a></span><spanclass="hspace"> </span><spanclass="RktVal">'</span><spanclass="RktVal">publisher</span><spanclass="hspace"> </span><spanclass="RktVal">'</span><spanclass="RktVal">foo</span><spanclass="hspace"> </span><spanclass="RktVal">'</span><spanclass="RktVal">participant</span><spanclass="RktPn">)</span></p></blockquote><p>Notice that the orientation of the role is the opposite of the
orientation of the endpoint.</p><p><divclass="SIntrapara"><blockquoteclass="SVInsetFlow"><tablecellspacing="0"class="boxed RBoxed"><tr><td><blockquoteclass="SubFlow"><divclass="RBackgroundLabel SIEHidden"><divclass="RBackgroundLabelInner"><p>type</p></div></div><pclass="RForeground"><aname="(def._((lib._marketplace/main..rkt)._.Orientation))"></a><spantitle="Provided from: marketplace, marketplace/sugar-untyped, marketplace/sugar-typed"><spanclass="RktSym"><ahref="#%28def._%28%28lib._marketplace%2Fmain..rkt%29._.Orientation%29%29"class="RktValLink"data-pltdoc="x">Orientation</a></span></span><spanclass="hspace"> </span>:<spanclass="hspace"> </span><spanclass="RktPn">(</span><spanclass="RktSym"><ahref="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><spanclass="hspace"> </span><spanclass="RktVal">'</span><spanclass="RktVal">publisher</span><spanclass="hspace"> </span><spanclass="RktVal">'</span><spanclass="RktVal">subscriber</span><spanclass="RktPn">)</span></p></blockquote></td></tr></table></blockquote></div><divclass="SIntrapara">Describes an endpoint’s orientation: will it be acting as a publisher
<spanclass="RktVal">'</span><spanclass="RktVal">publisher</span>) tend to use <spanclass="RktSym"><ahref="high-level-interface.html#%28def._%28%28lib._marketplace%2Fsugar-values..rkt%29._send-message%29%29"class="RktValLink"data-pltdoc="x">send-message</a></span> and tend to
(<spanclass="RktVal">'</span><spanclass="RktVal">subscriber</span>) tend to use <spanclass="RktSym"><ahref="high-level-interface.html#%28def._%28%28lib._marketplace%2Fsugar-values..rkt%29._send-feedback%29%29"class="RktValLink"data-pltdoc="x">send-feedback</a></span> and respond
to messages from publishers.</div></p><p><divclass="SIntrapara"><blockquoteclass="SVInsetFlow"><tablecellspacing="0"class="boxed RBoxed"><tr><td><blockquoteclass="SubFlow"><divclass="RBackgroundLabel SIEHidden"><divclass="RBackgroundLabelInner"><p>type</p></div></div><pclass="RForeground"><aname="(def._((lib._marketplace/main..rkt)._.Interest.Type))"></a><spantitle="Provided from: marketplace, marketplace/sugar-untyped, marketplace/sugar-typed"><spanclass="RktSym"><ahref="#%28def._%28%28lib._marketplace%2Fmain..rkt%29._.Interest.Type%29%29"class="RktValLink"data-pltdoc="x">InterestType</a></span></span><spanclass="hspace"> </span>:<spanclass="hspace"> </span><spanclass="RktPn">(</span><spanclass="RktSym"><ahref="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><spanclass="hspace"> </span><spanclass="RktVal">'</span><spanclass="RktVal">participant</span><spanclass="hspace"> </span><spanclass="RktVal">'</span><spanclass="RktVal">observer</span><spanclass="hspace"> </span><spanclass="RktVal">'</span><spanclass="RktVal">everything</span><spanclass="RktPn">)</span></p></blockquote></td></tr></table></blockquote></div><divclass="SIntrapara">Using interest-type <spanclass="RktVal">'</span><spanclass="RktVal">participant</span> in an endpoint’s role
indicates that the endpoint is intending to act as a genuine
participant in whatever protocol is associated with the endpoint and
its topic.</div></p><p>Using <spanclass="RktVal">'</span><spanclass="RktVal">observer</span> indicates that the endpoint is intended to
<spanstyle="font-style: italic">monitor</span> other ongoing (participant) conversations instead.
Observer endpoints receive presence and absence notifications about
participant endpoints, but participant endpoints only receive
notifications about other participant endpoints, and not about
observer endpoints.</p><p>The <spanclass="RktVal">'</span><spanclass="RktVal">observer</span> interest-type is intended to make it easier to
monitor resource demand and supply. The monitoring endpoints/processes
can react to changing demand by creating or destroying resources to
match.</p><p>Finally, the <spanclass="RktVal">'</span><spanclass="RktVal">everything</span> interest-type receives notifications
about presence and absence of <spanstyle="font-style: italic">all</span> the types of endpoint,
<spanclass="RktVal">'</span><spanclass="RktVal">participant</span>, <spanclass="RktVal">'</span><spanclass="RktVal">observer</span>, and <spanclass="RktVal">'</span><spanclass="RktVal">everything</span>.
Endpoints with interest-type <spanclass="RktVal">'</span><spanclass="RktVal">everything</span> are rare: they are
relevant for managing demand for <spanstyle="font-style: italic">observers</span>, as well as in some
cases of cross-layer presence/absence propagation. Most programs (and
even most drivers) will not need to use the <spanclass="RktVal">'</span><spanclass="RktVal">everything</span>
message that has been sent on a VM’s IPC facility.</div></p><p><divclass="SIntrapara"><blockquoteclass="SVInsetFlow"><tablecellspacing="0"class="boxed RBoxed"><tr><td><blockquoteclass="SubFlow"><divclass="RBackgroundLabel SIEHidden"><divclass="RBackgroundLabelInner"><p>struct</p></div></div><tablecellspacing="0"class="RForeground"><tr><td><spanclass="RktPn">(</span><spanclass="RktSym"><ahref="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><spanclass="hspace"> </span></td><td><aname="(def._((lib._marketplace/main..rkt)._presence-event-role))"></a><aname="(def._((lib._marketplace/main..rkt)._presence-event~3f))"></a><aname="(def._((lib._marketplace/main..rkt)._struct~3apresence-event))"></a><aname="(def._((lib._marketplace/main..rkt)._presence-event))"></a><spantitle="Provided from: marketplace"><spanclass="RktSym"><ahref="#%28def._%28%28lib._marketplace%2Fmain..rkt%29._presence-event%29%29"class="RktValLink"data-pltdoc="x">presence-event</a></span></span><spanclass="hspace"> </span><spanclass="RktPn">(</span><spanclass="RktSym">role</span><spanclass="RktPn">)</span></td></tr><tr><td><spanclass="hspace"> </span></td><td><spanclass="hspace"> </span></td><td><spanclass="RktPn">#:prefab</span><spanclass="RktPn">)</span></td></tr></table></blockquote></td></tr><tr><td><spanclass="hspace"> </span><spanclass="RktSym">role</span><spanclass="hspace"> </span>:<spanclass="hspace"> </span><spanclass="RktSym"><ahref="#%28def._%28%28lib._marketplace%2Fmain..rkt%29._.Role%29%29"class="RktValLink"data-pltdoc="x">Role</a></span></td></tr></table></blockquote></div><divclass="SIntrapara">Indicates the arrival of a new conversational partner: an endpoint
with a topic that intersects our own, with <spanclass="RktSym"><ahref="#%28def._%28%28lib._marketplace%2Fmain..rkt%29._.Orientation%29%29"class="RktValLink"data-pltdoc="x">Orientation</a></span>
opposite to our own.</div></p><p>The <spanclass="RktSym"><ahref="#%28def._%28%28lib._marketplace%2Fmain..rkt%29._presence-event-role%29%29"class="RktValLink"data-pltdoc="x">presence-event-role</a></span> describes the arriving peer, or more
peer. In particular, the <spanclass="RktSym"><ahref="#%28def._%28%28lib._marketplace%2Fmain..rkt%29._role-orientation%29%29"class="RktValLink"data-pltdoc="x">role-orientation</a></span> of the
<spanclass="RktSym"><ahref="#%28def._%28%28lib._marketplace%2Fmain..rkt%29._presence-event-role%29%29"class="RktValLink"data-pltdoc="x">presence-event-role</a></span> is the orientation that the <spanstyle="font-style: italic">peer</span>
supplied in its <spanclass="RktSym"><ahref="#%28def._%28%28lib._marketplace%2Fmain..rkt%29._add-endpoint%29%29"class="RktValLink"data-pltdoc="x">add-endpoint</a></span> structure.</p><p><divclass="SIntrapara"><blockquoteclass="SVInsetFlow"><tablecellspacing="0"class="boxed RBoxed"><tr><td><blockquoteclass="SubFlow"><divclass="RBackgroundLabel SIEHidden"><divclass="RBackgroundLabelInner"><p>struct</p></div></div><tablecellspacing="0"class="RForeground"><tr><td><spanclass="RktPn">(</span><spanclass="RktSym"><ahref="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><spanclass="hspace"> </span></td><td><aname="(def._((lib._marketplace/main..rkt)._absence-event-reason))"></a><aname="(def._((lib._marketplace/main..rkt)._absence-event-role))"></a><aname="(def._((lib._marketplace/main..rkt)._absence-event~3f))"></a><aname="(def._((lib._marketplace/main..rkt)._struct~3aabsence-event))"></a><aname="(def._((lib._marketplace/main..rkt)._absence-event))"></a><spantitle="Provided from: marketplace"><spanclass="RktSym"><ahref="#%28def._%28%28lib._marketplace%2Fmain..rkt%29._absence-event%29%29"class="RktValLink"data-pltdoc="x">absence-event</a></span></span><spanclass="hspace"> </span><spanclass="RktPn">(</span><spanclass="RktSym">role</span><spanclass="stt"></span><spanclass="RktSym">reason</span><spanclass="RktPn">)</span></td></tr><tr><td><spanclass="hspace"> </span></td><td><spanclass="hspace"> </span></td><td><spanclass="RktPn">#:prefab</span><spanclass="RktPn">)</span></td></tr></table></blockquote></td></tr><tr><td><spanclass="hspace"> </span><spanclass="RktSym">role</span><spanclass="hspace"> </span>:<spanclass="hspace"> </span><spanclass="RktSym"><ahref="#%28def._%28%28lib._marketplace%2Fmain..rkt%29._.Role%29%29"class="RktValLink"data-pltdoc="x">Role</a></span></td></tr><tr><td><spanclass="hspace"> </span><spanclass="RktSym">reason</span><spanclass="hspace"> </span>:<spanclass="hspace"> </span><spanclass="RktSym"><ahref="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><divclass="SIntrapara">Indicates the departure of an existing conversational partner, through
either an explicit <spanclass="RktSym"><ahref="high-level-interface.html#%28def._%28%28lib._marketplace%2Fsugar-values..rkt%29._delete-endpoint%29%29"class="RktValLink"data-pltdoc="x">delete-endpoint</a></span> action or the implicit
deleting of all of a process’s endpoints when a process exits.</div></p><p>The <spanclass="RktSym"><ahref="#%28def._%28%28lib._marketplace%2Fmain..rkt%29._absence-event-role%29%29"class="RktValLink"data-pltdoc="x">absence-event-role</a></span> describes the departing peer,
analogously to <spanclass="RktSym"><ahref="#%28def._%28%28lib._marketplace%2Fmain..rkt%29._presence-event-role%29%29"class="RktValLink"data-pltdoc="x">presence-event-role</a></span>.</p><p><divclass="SIntrapara"><blockquoteclass="SVInsetFlow"><tablecellspacing="0"class="boxed RBoxed"><tr><td><blockquoteclass="SubFlow"><divclass="RBackgroundLabel SIEHidden"><divclass="RBackgroundLabelInner"><p>struct</p></div></div><tablecellspacing="0"class="RForeground"><tr><td><spanclass="RktPn">(</span><spanclass="RktSym"><ahref="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><spanclass="hspace"> </span></td><td><aname="(def._((lib._marketplace/main..rkt)._message-event-message))"></a><aname="(def._((lib._marketplace/main..rkt)._message-event-role))"></a><aname="(def._((lib._marketplace/main..rkt)._message-event~3f))"></a><aname="(def._((lib._marketplace/main..rkt)._struct~3amessage-event))"></a><aname="(def._((lib._marketplace/main..rkt)._message-event))"></a><spantitle="Provided from: marketplace"><spanclass="RktSym"><ahref="#%28def._%28%28lib._marketplace%2Fmain..rkt%29._message-event%29%29"class="RktValLink"data-pltdoc="x">message-event</a></span></span><spanclass="hspace"> </span><spanclass="RktPn">(</span><spanclass="RktSym">role</span><spanclass="stt"></span><spanclass="RktSym">message</span><spanclass="RktPn">)</span></td></tr><tr><td><spanclass="hspace"> </span></td><td><spanclass="hspace"> </span></td><td><spanclass="RktPn">#:prefab</span><spanclass="RktPn">)</span></td></tr></table></blockquote></td></tr><tr><td><spanclass="hspace"> </span><spanclass="RktSym">role</span><spanclass="hspace"> </span>:<spanclass="hspace"> </span><spanclass="RktSym"><ahref="#%28def._%28%28lib._marketplace%2Fmain..rkt%29._.Role%29%29"class="RktValLink"data-pltdoc="x">Role</a></span></td></tr><tr><td><spanclass="hspace"> </span><spanclass="RktSym">message</span><spanclass="hspace"> </span>:<spanclass="hspace"> </span><spanclass="RktSym"><ahref="#%28def._%28%28lib._marketplace%2Fmain..rkt%29._.Message%29%29"class="RktValLink"data-pltdoc="x">Message</a></span></td></tr></table></blockquote></div><divclass="SIntrapara">Indicates the arrival of a message matching the topic pattern in the
in an <spanclass="RktSym"><ahref="high-level-interface.html#%28def._%28%28lib._marketplace%2Fsugar-values..rkt%29._at-meta-level%29%29"class="RktValLink"data-pltdoc="x">at-meta-level</a></span> structure, the action is to apply to
the process’s containing VM.</div></p><p><divclass="SIntrapara"><blockquoteclass="SVInsetFlow"><tablecellspacing="0"class="boxed RBoxed"><tr><td><tablecellspacing="0"class="together"><tr><td><blockquoteclass="SubFlow"><divclass="RBackgroundLabel SIEHidden"><divclass="RBackgroundLabelInner"><p>struct</p></div></div><tablecellspacing="0"class="RForeground"><tr><td><spanclass="RktPn">(</span><spanclass="RktSym"><ahref="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><spanclass="hspace"> </span></td><td><aname="(def._((lib._marketplace/main..rkt)._at-meta-level-preaction))"></a><aname="(def._((lib._marketplace/main..rkt)._at-meta-level~3f))"></a><aname="(def._((lib._marketplace/main..rkt)._struct~3aat-meta-level))"></a><aname="(def._((lib._marketplace/main..rkt)._at-meta-level))"></a><spantitle="Provided from: marketplace"><spanclass="RktSym"><ahref="high-level-interface.html#%28def._%28%28lib._marketplace%2Fsugar-values..rkt%29._at-meta-level%29%29"class="RktValLink"data-pltdoc="x">at-meta-level</a></span></span><spanclass="hspace"> </span><spanclass="RktPn">(</span><spanclass="RktSym">preaction</span><spanclass="RktPn">)</span></td></tr><tr><td><spanclass="hspace"> </span></td><td><spanclass="hspace"> </span></td><td><spanclass="RktPn">#:prefab</span><spanclass="RktPn">)</span></td></tr></table></blockquote></td></tr><tr><td><spanclass="hspace"> </span><spanclass="RktSym">preaction</span><spanclass="hspace"> </span>:<spanclass="hspace"> </span><spanclass="RktPn">(</span><spanclass="RktSym"><ahref="#%28def._%28%28lib._marketplace%2Fmain..rkt%29._.Pre.Action%29%29"class="RktValLink"data-pltdoc="x">PreAction</a></span><spanclass="hspace"> </span><spanclass="RktSym">State</span><spanclass="RktPn">)</span></td></tr></table></td></tr><tr><td><tablecellspacing="0"class="together"><tr><td><blockquoteclass="SubFlow"><divclass="RBackgroundLabel SIEHidden"><divclass="RBackgroundLabelInner"><p>type</p></div></div><pclass="RForeground"><aname="(def._((lib._marketplace/main..rkt)._.At.Meta.Level))"></a><spantitle="Provided from: marketplace"><spanclass="RktSym"><ahref="#%28def._%28%28lib._marketplace%2Fmain..rkt%29._.At.Meta.Level%29%29"class="RktValLink"data-pltdoc="x">AtMetaLevel</a></span></span><spanclass="hspace"> </span>:<spanclass="hspace"> </span><spanclass="RktPn">(</span><spanclass="RktSym"><ahref="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><spanclass="hspace"> </span><spanclass="RktPn">(</span><spanclass="RktSym">State</span><spanclass="RktPn">)</span><spanclass="hspace"> </span><spanclass="RktPn">(</span><spanclass="RktSym"><ahref="high-level-interface.html#%28def._%28%28lib._marketplace%2Fsugar-values..rkt%29._at-meta-level%29%29"class="RktValLink"data-pltdoc="x">at-meta-level</a></span><spanclass="hspace"> </span><spanclass="RktSym">State</span><spanclass="RktPn">)</span><spanclass="RktPn">)</span></p></blockquote></td></tr></table></td></tr></table></blockquote></div><divclass="SIntrapara">An <spanclass="RktSym"><ahref="high-level-interface.html#%28def._%28%28lib._marketplace%2Fsugar-values..rkt%29._at-meta-level%29%29"class="RktValLink"data-pltdoc="x">at-meta-level</a></span> structure wraps a plain action, and makes it
apply to the outer VM instead of the inner VM (the default).</div></p><p><divclass="SIntrapara"><blockquoteclass="SVInsetFlow"><tablecellspacing="0"class="boxed RBoxed"><tr><td><tablecellspacing="0"class="together"><tr><td><blockquoteclass="SubFlow"><divclass="RBackgroundLabel SIEHidden"><divclass="RBackgroundLabelInner"><p>struct</p></div></div><tablecellspacing="0"class="RForeground"><tr><td><spanclass="RktPn">(</span><spanclass="RktSym"><ahref="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><spanclass="hspace"> </span></td><td><aname="(def._((lib._marketplace/main..rkt)._yield-k))"></a><aname="(def._((lib._marketplace/main..rkt)._yield~3f))"></a><aname="(def._((lib._marketplace/main..rkt)._struct~3ayield))"></a><aname="(def._((lib._marketplace/main..rkt)._yield))"></a><spantitle="Provided from: marketplace"><spanclass="RktSym"><ahref="high-level-interface.html#%28form._%28%28lib._marketplace%2Fsugar-untyped..rkt%29._yield%29%29"class="RktStxLink"data-pltdoc="x">yield</a></span></span><spanclass="hspace"> </span><spanclass="RktPn">(</span><spanclass="RktSym">k</span><spanclass="RktPn">)</span></td></tr><tr><td><spanclass="hspace"> </span></td><td><spanclass="hspace"> </span></td><td><spanclass="RktPn">#:prefab</span><spanclass="RktPn">)</span></td></tr></table></blockquote></td></tr><tr><td><spanclass="hspace"> </span><spanclass="RktSym">k</span><spanclass="hspace"> </span>:<spanclass="hspace"> </span><spanclass="RktPn">(</span><spanclass="RktSym"><ahref="#%28def._%28%28lib._marketplace%2Fmain..rkt%29._.Interrupt.K%29%29"class="RktValLink"data-pltdoc="x">InterruptK</a></span><spanclass="hspace"> </span><spanclass="RktSym">State</span><spanclass="RktPn">)</span></td></tr></table></td></tr><tr><td><tablecellspacing="0"class="together"><tr><td><blockquoteclass="SubFlow"><divclass="RBackgroundLabel SIEHidden"><divclass="RBackgroundLabelInner"><p>type</p></div></div><pclass="RForeground"><aname="(def._((lib._marketplace/main..rkt)._.Yield))"></a><spantitle="Provided from: marketplace"><spanclass="RktSym"><ahref="#%28def._%28%28lib._marketplace%2Fmain..rkt%29._.Yield%29%29"class="RktValLink"data-pltdoc="x">Yield</a></span></span><spanclass="hspace"> </span>:<spanclass="hspace"> </span><spanclass="RktPn">(</span><spanclass="RktSym"><ahref="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><spanclass="hspace"> </span><spanclass="RktPn">(</span><spanclass="RktSym">State</span><spanclass="RktPn">)</span><spanclass="hspace"> </span><spanclass="RktPn">(</span><spanclass="RktSym"><ahref="high-level-interface.html#%28form._%28%28lib._marketplace%2Fsugar-untyped..rkt%29._yield%29%29"class="RktStxLink"data-pltdoc="x">yield</a></span><spanclass="hspace"> </span><spanclass="RktSym">State</span><spanclass="RktPn">)</span><spanclass="RktPn">)</span></p></blockquote></td></tr></table></td></tr></table></blockquote></div><divclass="SIntrapara">Because current VM implementations are cooperatively scheduled, it can
using a <spanclass="RktSym"><ahref="high-level-interface.html#%28form._%28%28lib._marketplace%2Fsugar-untyped..rkt%29._yield%29%29"class="RktStxLink"data-pltdoc="x">yield</a></span> action. When control returns to the yielding
process, the <spanclass="RktSym"><ahref="#%28def._%28%28lib._marketplace%2Fmain..rkt%29._yield-k%29%29"class="RktValLink"data-pltdoc="x">yield-k</a></span> is invoked.</div></p><h5>3.4.1<tt> </tt><aname="(part._endpoints-and-messages)"></a>Endpoints and Messages</h5><p><divclass="SIntrapara"><blockquoteclass="SVInsetFlow"><tablecellspacing="0"class="boxed RBoxed"><tr><td><tablecellspacing="0"class="together"><tr><td><blockquoteclass="SubFlow"><divclass="RBackgroundLabel SIEHidden"><divclass="RBackgroundLabelInner"><p>struct</p></div></div><tablecellspacing="0"class="RForeground"><tr><td><spanclass="RktPn">(</span><spanclass="RktSym"><ahref="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><spanclass="hspace"> </span></td><td><aname="(def._((lib._marketplace/main..rkt)._add-endpoint-handler))"></a><aname="(def._((lib._marketplace/main..rkt)._add-endpoint-role))"></a><aname="(def._((lib._marketplace/main..rkt)._add-endpoint-pre-eid))"></a><aname="(def._((lib._marketplace/main..rkt)._add-endpoint~3f))"></a><aname="(def._((lib._marketplace/main..rkt)._struct~3aadd-endpoint))"></a><aname="(def._((lib._marketplace/main..rkt)._add-endpoint))"></a><spantitle="Provided from: marketplace"><spanclass="RktSym"><ahref="#%28def._%28%28lib._marketplace%2Fmain..rkt%29._add-endpoint%29%29"class="RktValLink"data-pltdoc="x">add-endpoint</a></span></span><spanclass="hspace"> </span><spanclass="RktPn">(</span><spanclass="RktSym">pre-eid</span><spanclass="stt"></span><spanclass="RktSym">role</span><spanclass="stt"></span><spanclass="RktSym">handler</span><spanclass="RktPn">)</span></td></tr><tr><td><spanclass="hspace"> </span></td><td><spanclass="hspace"> </span></td><td><spanclass="RktPn">#:prefab</span><spanclass="RktPn">)</span></td></tr></table></blockquote></td></tr><tr><td><spanclass="hspace"> </span><spanclass="RktSym">pre-eid</span><spanclass="hspace"> </span>:<spanclass="hspace"> </span><spanclass="RktSym"><ahref="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><spanclass="hspace"> </span><spanclass="RktSym">role</span><spanclass="hspace"> </span>:<spanclass="hspace"> </span><spanclass="RktSym"><ahref="#%28def._%28%28lib._marketplace%2Fmain..rkt%29._.Role%29%29"class="RktValLink"data-pltdoc="x">Role</a></span></td></tr><tr><td><spanclass="hspace"> </span><spanclass="RktSym">handler</span><spanclass="hspace"> </span>:<spanclass="hspace"> </span><spanclass="RktPn">(</span><spanclass="RktSym"><ahref="#%28def._%28%28lib._marketplace%2Fmain..rkt%29._.Handler%29%29"class="RktValLink"data-pltdoc="x">Handler</a></span><spanclass="hspace"> </span><spanclass="RktSym">State</span><spanclass="RktPn">)</span></td></tr></table></td></tr><tr><td><tablecellspacing="0"class="together"><tr><td><blockquoteclass="SubFlow"><divclass="RBackgroundLabel SIEHidden"><divclass="RBackgroundLabelInner"><p>type</p></div></div><pclass="RForeground"><aname="(def._((lib._marketplace/main..rkt)._.Add.Endpoint))"></a><spantitle="Provided from: marketplace"><spanclass="RktSym"><ahref="#%28def._%28%28lib._marketplace%2Fmain..rkt%29._.Add.Endpoint%29%29"class="RktValLink"data-pltdoc="x">AddEndpoint</a></span></span><spanclass="hspace"> </span>:<spanclass="hspace"> </span><spanclass="RktPn">(</span><spanclass="RktSym"><ahref="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><spanclass="hspace"> </span><spanclass="RktPn">(</span><spanclass="RktSym">State</span><spanclass="RktPn">)</span><spanclass="hspace"> </span><spanclass="RktPn">(</span><spancla
events pertaining to the given role occur, the <spanclass="RktSym"><ahref="#%28def._%28%28lib._marketplace%2Fmain..rkt%29._.Handler%29%29"class="RktValLink"data-pltdoc="x">Handler</a></span> is
invoked.<spanclass="NoteBox"><spanclass="NoteContent">If invoked <spanclass="RktSym"><ahref="high-level-interface.html#%28def._%28%28lib._marketplace%2Fsugar-values..rkt%29._at-meta-level%29%29"class="RktValLink"data-pltdoc="x">at-meta-level</a></span>, subscribes to events
in the containing VM’s container.</span></span></div></p><p>The name of the new endpoint will be the <spanclass="RktSym">pre-eid</span>; it must be
unique within the current process, but otherwise can be any value at
all. If the endpoint’s name matches an existing endpoint, and the new
role is the same as the existing endpoint’s role, the handler function
is <spanstyle="font-style: italic">replaced</span> in the existing endpoint.</p><p>To delete an endpoint, perform a <spanclass="RktSym"><ahref="high-level-interface.html#%28def._%28%28lib._marketplace%2Fsugar-values..rkt%29._delete-endpoint%29%29"class="RktValLink"data-pltdoc="x">delete-endpoint</a></span> action built
with the name of the endpoint to delete.</p><p><divclass="SIntrapara"><blockquoteclass="SVInsetFlow"><tablecellspacing="0"class="boxed RBoxed"><tr><td><tablecellspacing="0"class="together"><tr><td><blockquoteclass="SubFlow"><divclass="RBackgroundLabel SIEHidden"><divclass="RBackgroundLabelInner"><p>struct</p></div></div><tablecellspacing="0"class="RForeground"><tr><td><spanclass="RktPn">(</span><spanclass="RktSym"><ahref="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><spanclass="hspace"> </span></td><td><aname="(def._((lib._marketplace/main..rkt)._delete-endpoint-reason))"></a><aname="(def._((lib._marketplace/main..rkt)._delete-endpoint-pre-eid))"></a><aname="(def._((lib._marketplace/main..rkt)._delete-endpoint~3f))"></a><aname="(def._((lib._marketplace/main..rkt)._struct~3adelete-endpoint))"></a><aname="(def._((lib._marketplace/main..rkt)._delete-endpoint))"></a><spantitle="Provided from: marketplace"><spanclass="RktSym"><ahref="high-level-interface.html#%28def._%28%28lib._marketplace%2Fsugar-values..rkt%29._delete-endpoint%29%29"class="RktValLink"data-pltdoc="x">delete-endpoint</a></span></span><spanclass="hspace"> </span><spanclass="RktPn">(</span><spanclass="RktSym">pre-eid</span><spanclass="stt"></span><spanclass="RktSym">reason</span><spanclass="RktPn">)</span></td></tr><tr><td><spanclass="hspace"> </span></td><td><spanclass="hspace"> </span></td><td><spanclass="RktPn">#:prefab</span><spanclass="RktPn">)</span></td></tr></table></blockquote></td></tr><tr><td><spanclass="hspace"> </span><spanclass="RktSym">pre-eid</span><spanclass="hspace"> </span>:<spanclass="hspace"> </span><spanclass="RktSym"><ahref="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><spanclass="hspace"> </span><spanclass="RktSym">reason</span><spanclass="hspace"> </span>:<spanclass="hspace"> </span><spanclass="RktSym"><ahref="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></td></tr><tr><td><tablecellspacing="0"class="together"><tr><td><blockquoteclass="SubFlow"><divclass="RBackgroundLabel SIEHidden"><divclass="RBackgroundLabelInner"><p>type</p></div></div><pclass="RForeground"><aname="(def._((lib._marketplace/main..rkt)._.Delete.Endpoint))"></a><spantitle="Provided from: marketplace"><spanclass="RktSym"><ahref="#%28def._%28%28lib._marketplace%2Fmain..rkt%29._.Delete.Endpoint%29%29"class="RktValLink"data-pltdoc="x">DeleteEndpoint</a></span></span><spanclass="hspace"> </span>:<spanclass="hspace"> </span><spanclass="RktSym"><ahref="high-level-interface.html#%28def._%28%28lib._marketplace%2Fsugar-values..rkt%29._delete-endpoint%29%29"class="RktValLink"data-pltdoc="x">delete-endpoint</a></span></p></blockquote></td></tr></table></td></tr></table></blockquote></div><divclass="SIntrapara">Deletes an existing endpoint named <spanclass="RktSym">pre-eid</span>. The given
<spanclass="RktSym"><ahref="#%28def._%28%28lib._marketplace%2Fmain..rkt%29._absence-event%29%29"class="RktValLink"data-pltdoc="x">absence-event</a></span>.</div></p><p>If no specific reason is needed, it is conventional to supply
<spanclass="RktVal">#f</span> as the <spanclass="RktSym"><ahref="#%28def._%28%28lib._marketplace%2Fmain..rkt%29._delete-endpoint-reason%29%29"class="RktValLink"data-pltdoc="x">delete-endpoint-reason</a></span>. See also the
function from <spanclass="RktSym">marketplace/sugar-values</span>.</p><p><divclass="SIntrapara"><blockquoteclass="SVInsetFlow"><tablecellspacing="0"class="boxed RBoxed"><tr><td><tablecellspacing="0"class="together"><tr><td><blockquoteclass="SubFlow"><divclass="RBackgroundLabel SIEHidden"><divclass="RBackgroundLabelInner"><p>struct</p></div></div><tablecellspacing="0"class="RForeground"><tr><td><spanclass="RktPn">(</span><spanclass="RktSym"><ahref="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><spanclass="hspace"> </span></td><td><aname="(def._((lib._marketplace/main..rkt)._send-message-orientation))"></a><aname="(def._((lib._marketplace/main..rkt)._send-message-body))"></a><aname="(def._((lib._marketplace/main..rkt)._send-message~3f))"></a><aname="(def._((lib._marketplace/main..rkt)._struct~3asend-message))"></a><aname="(def._((lib._marketplace/main..rkt)._send-message))"></a><spantitle="Provided from: marketplace"><spanclass="RktSym"><ahref="high-level-interface.html#%28def._%28%28lib._marketplace%2Fsugar-values..rkt%29._send-message%29%29"class="RktValLink"data-pltdoc="x">send-message</a></span></span><spanclass="hspace"> </span><spanclass="RktPn">(</span><spanclass="RktSym">body</span><spanclass="stt"></span><spanclass="RktSym">orientation</span><spanclass="RktPn">)</span></td></tr><tr><td><spanclass="hspace"> </span></td><td><spanclass="hspace"> </span></td><td><spanclass="RktPn">#:prefab</span><spanclass="RktPn">)</span></td></tr></table></blockquote></td></tr><tr><td><spanclass="hspace"> </span><spanclass="RktSym">body</span><spanclass="hspace"> </span>:<spanclass="hspace"> </span><spanclass="RktSym"><ahref="#%28def._%28%28lib._marketplace%2Fmain..rkt%29._.Message%29%29"class="RktValLink"data-pltdoc="x">Message</a></span></td></tr><tr><td><spanclass="hspace"> </span><spanclass="RktSym">orientation</span><spanclass="hspace"> </span>:<spanclass="hspace"> </span><spanclass="RktSym"><ahref="#%28def._%28%28lib._marketplace%2Fmain..rkt%29._.Orientation%29%29"class="RktValLink"data-pltdoc="x">Orientation</a></span></td></tr></table></td></tr><tr><td><tablecellspacing="0"class="together"><tr><td><blockquoteclass="SubFlow"><divclass="RBackgroundLabel SIEHidden"><divclass="RBackgroundLabelInner"><p>type</p></div></div><pclass="RForeground"><aname="(def._((lib._marketplace/main..rkt)._.Send.Message))"></a><spantitle="Provided from: marketplace"><spanclass="RktSym"><ahref="#%28def._%28%28lib._marketplace%2Fmain..rkt%29._.Send.Message%29%29"class="RktValLink"data-pltdoc="x">SendMessage</a></span></span><spanclass="hspace"> </span>:<spanclass="hspace"> </span><spanclass="RktSym"><ahref="high-level-interface.html#%28def._%28%28lib._marketplace%2Fsugar-values..rkt%29._send-message%29%29"class="RktValLink"data-pltdoc="x">send-message</a></span></p></blockquote></td></tr></table></td></tr></table></blockquote></div><divclass="SIntrapara">Sends a message to peers.<spanclass="NoteBox"><spanclass="NoteContent">Or, if <spanclass="RktSym"><ahref="high-level-interface.html#%28def._%28%28lib._marketplace%2Fsugar-values..rkt%29._at-meta-level%29%29"class="RktValLink"data-pltdoc="x">at-meta-level</a></span>, peers of
the containing VM.</span></span> The given <spanclass="RktSym"><ahref="#%28def._%28%28lib._marketplace%2Fmain..rkt%29._.Orientation%29%29"class="RktValLink"data-pltdoc="x">Orientation</a></span> should describe the
some publisher, it will be <spanclass="RktVal">'</span><spanclass="RktVal">subscriber</span>.
See also the <spanclass="RktSym"><ahref="high-level-interface.html#%28def._%28%28lib._marketplace%2Fsugar-values..rkt%29._send-message%29%29"class="RktValLink"data-pltdoc="x">send-message</a></span> and
<spanclass="RktSym"><ahref="high-level-interface.html#%28def._%28%28lib._marketplace%2Fsugar-values..rkt%29._send-feedback%29%29"class="RktValLink"data-pltdoc="x">send-feedback</a></span> convenience functions from
wrapped in an <spanclass="RktSym"><ahref="high-level-interface.html#%28def._%28%28lib._marketplace%2Fsugar-values..rkt%29._at-meta-level%29%29"class="RktValLink"data-pltdoc="x">at-meta-level</a></span>, the new process will instead be
a sibling of the creating process’s VM.</span></span>. The <spanclass="RktSym"><ahref="#%28def._%28%28lib._marketplace%2Fmain..rkt%29._spawn-k%29%29"class="RktValLink"data-pltdoc="x">spawn-k</a></span> runs in
PID of the new process.</div></p><p>The <spanclass="RktSym"><ahref="#%28def._%28%28lib._marketplace%2Fmain..rkt%29._spawn-spec%29%29"class="RktValLink"data-pltdoc="x">spawn-spec</a></span> describes the new process to be created. Its
<spanclass="RktSym"><ahref="#%28def._%28%28lib._marketplace%2Fmain..rkt%29._process-spec-boot%29%29"class="RktValLink"data-pltdoc="x">process-spec-boot</a></span> field is a function taking the PID of the
complexity: see <spanclass="RktSym"><ahref="high-level-interface.html#%28form._%28%28lib._marketplace%2Fsugar-typed..rkt%29._spawn~3a%29%29"class="RktStxLink"data-pltdoc="x">spawn:</a></span> for an easier-to-use, higher-level
approach.</p><p><divclass="SIntrapara"><blockquoteclass="SVInsetFlow"><tablecellspacing="0"class="boxed RBoxed"><tr><td><tablecellspacing="0"class="together"><tr><td><blockquoteclass="SubFlow"><divclass="RBackgroundLabel SIEHidden"><divclass="RBackgroundLabelInner"><p>struct</p></div></div><tablecellspacing="0"class="RForeground"><tr><td><spanclass="RktPn">(</span><spanclass="RktSym"><ahref="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><spanclass="hspace"> </span></td><td><aname="(def._((lib._marketplace/main..rkt)._quit-reason))"></a><aname="(def._((lib._marketplace/main..rkt)._quit-pid))"></a><aname="(def._((lib._marketplace/main..rkt)._quit~3f))"></a><aname="(def._((lib._marketplace/main..rkt)._struct~3aquit))"></a><aname="(def._((lib._marketplace/main..rkt)._quit))"></a><spantitle="Provided from: marketplace"><spanclass="RktSym"><ahref="high-level-interface.html#%28def._%28%28lib._marketplace%2Fsugar-values..rkt%29._quit%29%29"class="RktValLink"data-pltdoc="x">quit</a></span></span><spanclass="hspace"> </span><spanclass="RktPn">(</span><spanclass="RktSym">pid</span><spanclass="stt"></span><spanclass="RktSym">reason</span><spanclass="RktPn">)</span></td></tr><tr><td><spanclass="hspace"> </span></td><td><spanclass="hspace"> </span></td><td><spanclass="RktPn">#:prefab</span><spanclass="RktPn">)</span></td></tr></table></blockquote></td></tr><tr><td><spanclass="hspace"> </span><spanclass="RktSym">pid</span><spanclass="hspace"> </span>:<spanclass="hspace"> </span><spanclass="RktPn">(</span><spanclass="RktSym"><ahref="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><spanclass="hspace"> </span><spanclass="RktSym"><ahref="#%28def._%28%28lib._marketplace%2Fmain..rkt%29._.P.I.D%29%29"class="RktValLink"data-pltdoc="x">PID</a></span><spanclass="RktPn">)</span></td></tr><tr><td><spanclass="hspace"> </span><spanclass="RktSym">reason</span><spanclass="hspace"> </span>:<spanclass="hspace"> </span><spanclass="RktSym"><ahref="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></td></tr><tr><td><tablecellspacing="0"class="together"><tr><td><blockquoteclass="SubFlow"><divclass="RBackgroundLabel SIEHidden"><divclass="RBackgroundLabelInner"><p>type</p></div></div><pclass="RForeground"><aname="(def._((lib._marketplace/main..rkt)._.Quit))"></a><spantitle="Provided from: marketplace"><spanclass="RktSym"><ahref="#%28def._%28%28lib._marketplace%2Fmain..rkt%29._.Quit%29%29"class="RktValLink"data-pltdoc="x">Quit</a></span></span><spanclass="hspace"> </span>:<spanclass="hspace"> </span><spanclass="RktSym"><ahref="high-level-interface.html#%28def._%28%28lib._marketplace%2Fsugar-values..rkt%29._quit%29%29"class="RktValLink"data-pltdoc="x">quit</a></span></p></blockquote></td></tr></table></td></tr></table></blockquote></div><divclass="SIntrapara">Kills a sibling process.<spanclass="NoteBox"><spanclass="NoteContent">Or, if <spanclass="RktSym"><ahref="high-level-interface.html#%28def._%28%28lib._marketplace%2Fsugar-values..rkt%29._at-meta-level%29%29"class="RktValLink"data-pltdoc="x">at-meta-level</a></span>, a sibling
process of the containing VM.</span></span> If <spanclass="RktSym"><ahref="#%28def._%28%28lib._marketplace%2Fmain..rkt%29._quit-pid%29%29"class="RktValLink"data-pltdoc="x">quit-pid</a></span> is <spanclass="RktVal">#f</span>,
PID. The <spanclass="RktSym"><ahref="#%28def._%28%28lib._marketplace%2Fmain..rkt%29._quit-reason%29%29"class="RktValLink"data-pltdoc="x">quit-reason</a></span> is passed on to peers of
<spanclass="RktSym"><ahref="#%28def._%28%28lib._marketplace%2Fmain..rkt%29._absence-event%29%29"class="RktValLink"data-pltdoc="x">absence-event</a></span>, just as if each active endpoint were deleted
<spanclass="RktVal">#f</span> as the <spanclass="RktSym"><ahref="#%28def._%28%28lib._marketplace%2Fmain..rkt%29._quit-reason%29%29"class="RktValLink"data-pltdoc="x">quit-reason</a></span>.</p><p><divclass="SIntrapara"><blockquoteclass="SVInsetFlow"><tablecellspacing="0"class="boxed RBoxed"><tr><td><blockquoteclass="SubFlow"><divclass="RBackgroundLabel SIEHidden"><divclass="RBackgroundLabelInner"><p>type</p></div></div><pclass="RForeground"><aname="(def._((lib._marketplace/main..rkt)._.P.I.D))"></a><spantitle="Provided from: marketplace"><spanclass="RktSym"><ahref="#%28def._%28%28lib._marketplace%2Fmain..rkt%29._.P.I.D%29%29"class="RktValLink"data-pltdoc="x">PID</a></span></span><spanclass="hspace"> </span>:<spanclass="hspace"> </span><spanclass="RktSym"><ahref="http://docs.racket-lang.org/ts-reference/type-ref.html#%28form._%28%28lib._typed-racket%2Fbase-env%2Fbase-types..rkt%29._.Number%29%29"class="RktStxLink"data-pltdoc="x">Number</a></span></p></blockquote></td></tr></table></blockquote></div><divclass="SIntrapara">In the current VM implementations, process IDs are simply numbers.
PIDs are scoped to and allocated by each individual VM instance.</div></p><divclass="navsetbottom"><spanclass="navleft"> </span><spanclass="navright"> <ahref="high-level-interface.html"title="backward to "2 High-level interface""data-pltdoc="x">← prev</a> <ahref="index.html"title="up to "Marketplace: Network-Aware Programming""data-pltdoc="x">up</a> <ahref="Drivers.html"title="forward to "4 Drivers""data-pltdoc="x">next →</a></span> </div></div></div><divid="contextindicator"> </div></body></html>