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Add call/ec' and let/ec'.

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Based on a patch by Nala Ginrut <nalaginrut@gmail.com>,
with suggestions from Mark H. Weaver.

* module/ice-9/control.scm (call-with-escape-continuation, call/ec): New
  procedures.
  (let-escape-continuation, let/ec): New macros.
* module/ice-9/futures.scm (let/ec): Remove.
* test-suite/tests/control.test ("escape-only continuations")["call/ec",
  "let/ec"]: New tests.
* doc/ref/api-control.texi (Prompt Primitives): Document `call/ec',
  `let/ec', and their long names.
This commit is contained in:
Ludovic Courtès 2013-04-04 14:14:25 +08:00
parent d888b53168
commit 55e26a49db
4 changed files with 107 additions and 15 deletions
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30
test-suite/tests/control.test
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@ -1,7 +1,7 @@
;;;; -*- scheme -*-
;;;; control.test --- test suite for delimited continuations
;;;;
;;;; Copyright (C) 2010, 2011 Free Software Foundation, Inc.
;;;; Copyright (C) 2010, 2011, 2013 Free Software Foundation, Inc.
;;;;
;;;; This library is free software; you can redistribute it and/or
;;;; modify it under the terms of the GNU Lesser General Public
@ -20,6 +20,7 @@
(define-module (test-suite test-control)
#:use-module (ice-9 control)
#:use-module (system vm vm)
#:use-module (srfi srfi-1)
#:use-module (srfi srfi-11)
#:use-module (test-suite lib))
@ -77,7 +78,32 @@
(abort 'foo 'bar 'baz)
(error "unexpected exit"))
(lambda (k . args)
args)))))
args))))
(pass-if-equal "call/ec" '(0 1 2) ; example from the manual
(let ((prefix
(lambda (x lst)
(call/ec
(lambda (return)
(fold (lambda (element prefix)
(if (equal? element x)
(return (reverse prefix))
(cons element prefix)))
'()
lst))))))
(prefix 'a '(0 1 2 a 3 4 5))))
(pass-if-equal "let/ec" '(0 1 2)
(let ((prefix
(lambda (x lst)
(let/ec return
(fold (lambda (element prefix)
(if (equal? element x)
(return (reverse prefix))
(cons element prefix)))
'()
lst)))))
(prefix 'a '(0 1 2 a 3 4 5)))))
;;; And the case in which the compiler has to reify the continuation.
(with-test-prefix/c&e "reified continuations"