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This module provides some syntactic sugar to Marc Feeley's continuation interface. In this interface, continuations are a datatype separate from procedures. Hence it provides a continuation? predicate. I've stripped the prefix from the procedures continuation-capture and continuation-graft and renamed continuation-return throw. This latter procedure is accompanied in this module by a macro named catch, so that the usual catch-throw-semantics of other languages is available. For example, a typical use pattern of this module is as follows
(catch k ... (if ... (throw k val) ...))
But note, that in this pattern, k is a Scheme object of type continuation, and like every Scheme object it has indefinite extent, hence can be exported, saved in other data-structures etc. So this pattern is much more powerful than the corresponding pattern in other languages.
Two other procedures are provided as well, continuation->procedure, which does what the name says, and continuations, which provides offline documentation to the module. Like in modules written in the design-by-contract style, the call (continuations) lists the exported symbols, and (continuations sym) provides documentation of the exported symbol sym.
continuations[procedure] (continuations [sym])
continuation?[procedure] (continuation? xpr)
continuation->procedure[procedure] (continuation->procedure cont)
transforms a continuation into a procedure
capture[procedure] (capture proc)
The same as call/cc but with a different datatype: Captures the current continuation as a continuation datatype (contrary to a procedure datatype in call/cc) and calls proc with that continuation as its only argument.
graft[procedure] (graft cont thunk)
tail-calls thunk with the implicit continuation cont.
throw[procedure] (throw cont . vals)
throws the values vals to the continuation cont.
catch[syntax] (catch cont xpr . xprs)
The same as let/cc of miscmacros but with a different datatype: Binds the cont variable to the current continuation as a continuation and executes the body xpr . xprs in this context.
May 25, 2013
Copyright (c) 2013, Juergen Lorenz All rights reserved.
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- initial import