--- layout: default title: "Throwing" parent: Abnormal ancestor: Funcons-beta --- [Funcons-beta] : [Throwing.cbs] ----------------------------- ### Throwing 
[
  Datatype throwing
  Funcon   thrown
  Funcon   finalise-throwing
  Funcon   throw
  Funcon   handle-thrown
  Funcon   handle-recursively
  Funcon   catch-else-throw
]
Meta-variables
  R, S, T, T′, T′′ <: values
Datatype
  throwing ::= thrown(_:values)
thrown(V) is a reason for abrupt termination. 
Funcon
  finalise-throwing(X:=>T) : =>T|null-type
   ~> finalise-abrupting(X)
finalise-throwing(X) handles abrupt termination of X due to executing throw(V). 
Funcon
  throw(V:T) : =>empty-type
   ~> abrupt(thrown(V))
throw(V) abruptly terminates all enclosing computations uTil it is handled. 
Funcon
  handle-thrown(_:T′=>T, _:T′′=>T) : T′=>T
handle-thrown(X, Y) first evaluates X. If X terminates normally with value V, then V is returned and Y is ignored. If X terminates abruptly with a thrown eTity having value V, then Y is executed with V as given value. handle-thrown(X, Y) is associative, with throw(given) as unit. handle-thrown(X, else(Y, throw(given))) ensures that if Y fails, the thrown value is re-thrown. 
Rule
                    X --abrupted( )-> X′
  --------------------------------------------------------
  handle-thrown(X, Y) --abrupted( )-> handle-thrown(X′, Y)
Rule
    X --abrupted(thrown(V′′:values))-> X′
  ----------------------------------------------
  handle-thrown(X, Y) --abrupted( )-> give(V′′, Y)
Rule
                    X --abrupted(V′:~throwing)-> X′
  ---------------------------------------------------------
  handle-thrown(X, Y) --abrupted(V′)-> handle-thrown(X′, Y)
Rule
  handle-thrown(V:T, Y) ~> V
Funcon
  handle-recursively(X:S=>T, Y:R=>T) : S=>T
    ~> handle-thrown(X, else(handle-recursively(Y, Y), throw(given)))
handle-recursively(X, Y) behaves similarly to handle-thrown(X, Y), except that another copy of the handler attempts to handle any values thrown by Y. Thus, many thrown values may get handled by the same handler. 
Funcon
  catch-else-throw(P:values, Y:=>T) : =>T
    ~> else(case-match(P, Y), throw(given))
handle-thrown(X, catch-else-throw(P, Y)) handles those values thrown by X that match pattern P. Other thrown values are re-thrown. ____ From the [PLanCompS Project] | [CBS-beta issues...] | [Suggest an improvement...] [Throwing.cbs]: Throwing.cbs "CBS SOURCE FILE" [Funcons-beta]: /CBS-beta/docs/Funcons-beta "FUNCONS-BETA" [Unstable-Funcons-beta]: /CBS-beta/docs/Unstable-Funcons-beta "UNSTABLE-FUNCONS-BETA" [Languages-beta]: /CBS-beta/docs/Languages-beta "LANGUAGES-BETA" [Unstable-Languages-beta]: /CBS-beta/docs/Unstable-Languages-beta "UNSTABLE-LANGUAGES-BETA" [CBS-beta]: /CBS-beta "CBS-BETA" [PLanCompS Project]: https://plancomps.github.io "PROGRAMMING LANGUAGE COMPONENTS AND SPECIFICATIONS PROJECT HOME PAGE" [CBS-beta issues...]: https://github.com/plancomps/CBS-beta/issues "CBS-BETA ISSUE REPORTS ON GITHUB" [Suggest an improvement...]: mailto:plancomps@gmail.com?Subject=CBS-beta%20-%20comment&Body=Re%3A%20CBS-beta%20specification%20at%20Computations/Abnormal/Throwing/Throwing.cbs%0A%0AComment/Query/Issue/Suggestion%3A%0A%0A%0ASignature%3A%0A "GENERATE AN EMAIL TEMPLATE"