--- layout: default title: "Controlling" parent: Abnormal ancestor: Funcons-beta --- [Funcons-beta] : [Controlling.cbs] ----------------------------- ### Controlling 
[
  Datatype continuations
  Funcon   continuation
  Entity   plug-signal
  Funcon   hole
  Funcon   resume-continuation
  Entity   control-signal
  Funcon   control
  Funcon   delimit-current-continuation  Alias delimit-cc
]
Meta-variables
  T, T1, T2 <: values
Datatype
  continuations(T1,T2) ::= continuation(_:abstractions(()=>T2))
continuations(T1, T2) consists of abstractions whose bodies contain a hole, and which will normally compute a value of type T2 when the hole is plugged with a value of type T1. 
Entity
  _ --plug-signal(V?:values?)-> _
A plug-signal contains the value to be filled into a hole in a continuation, thereby allowing a continuation to resume. 
Funcon
  hole : =>values
A hole in a term cannot proceed until it receives a plug-signal containing a value to plug the hole. 
Rule
 hole --plug-signal(V)-> V
Funcon
  resume-continuation(K:continuations(T1, T2), V:T1) : =>T2
resume-continuation(K, V) resumes a continuation K by plugging the value V into the hole in the continuation. 
Rule
                  X --plug-signal(V)-> X′
 ---------------------------------------------------------------------------
 resume-continuation(continuation(abstraction(X)), V:T) --plug-signal()-> X′
Entity
  _ --control-signal(F?:(functions(continuations(T1, T2), T2))?)-> _
A control-signal contains the function to which control is about to be passed by the enclosing delimit-current-continuation(X). 
Funcon
  control(F:functions(continuations(T1, T2), T2)) : =>T1
control(F) emits a control-signal that, when handled by an enclosing delimit-current-continuation(X), will apply F to the current continuation of control(F), (rather than proceeding with that current continuation). 
Rule
  control(F:functions(_,_)) --control-signal(F)-> hole
Funcon
  delimit-current-continuation(X:=>T) : =>T
Alias
  delimit-cc = delimit-current-continuation
delimit-current-continuation(X) delimits the scope of captured continuations. 
Rule
  delimit-current-continuation(V:T) ~> V
Rule
                         X --control-signal( )-> X′
  -----------------------------------------------------
  delimit-current-continuation(X) --control-signal( )->
    delimit-current-continuation(X′)
Rule
                         X --control-signal(F)-> X′
  ------------------------------------------------------------------
  delimit-current-continuation(X) --control-signal( )->
    delimit-current-continuation(apply(F, continuation closure(X′)))
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