On Wed, 2013-03-27 at 22:14 +0100, Ludovic Courtès wrote:
> Sounds good to me, but can you also (1) add doc, probably under “Prompt
> Primitives”, with cross-refs from the “Exceptions” section, and (2)
> write a ChangeLog-style commit log?
>
> Thanks,
> Ludo’.
>
>
Add call/ec and let/ec to (ice-9 control) with docs in the manual.
Thanks!
>From 0c899e96d9667a88ceb17cfbcdedf3e18aeef21c Mon Sep 17 00:00:00 2001
From: Nala Ginrut <nalagin...@gmail.com>
Date: Thu, 4 Apr 2013 14:14:25 +0800
Subject: [PATCH] Add escape continuation with docs
* ref/api-control.texi: Add docs
* ice-9/control.scm: Add let/ec and call/ec
* ice-9/futures.scm: Remove the old let/ec implementation.
---
doc/ref/api-control.texi | 23 +++++++++++++++++++++++
module/ice-9/control.scm | 27 +++++++++++++++++++++++++--
module/ice-9/futures.scm | 11 +----------
3 files changed, 49 insertions(+), 12 deletions(-)
diff --git a/doc/ref/api-control.texi b/doc/ref/api-control.texi
index 320812d..9ddeeb0 100644
--- a/doc/ref/api-control.texi
+++ b/doc/ref/api-control.texi
@@ -577,6 +577,29 @@ Before moving on, we should mention that if the handler of a prompt is a
that prompt will not cause a continuation to be reified. This can be an
important efficiency consideration to keep in mind.
+@deffn {Scheme Procedure} call/ec proc
+'ec' stands for escape-continuation, or so-called 'one-shot' continuation.
+@var{call/ec} is equivalent to call-with-escape-continuation.
+A continuation obtained from call/ec is actually a kind of prompt. @var{call/ec}
+is often an easy replacement for @var{call/cc} to improve performance.
+More details read @uref{http://www.cs.indiana.edu/~bruggema/one-shots-abstract.html,
+Representing control in the presence of one-shot continuations}.
+@end deffn
+
+@deffn {Scheme Syntax} let/ec k body
+Equivalent to (call/ec (lambda (k) body ...)).
+@end deffn
+
+@example
+(use-module (ice-9 control))
+
+(call/ec (lambda (return)
+ (return 123)))
+
+(let/ec return (return 123))
+@end example
+
+
@node Shift and Reset
@subsubsection Shift, Reset, and All That
diff --git a/module/ice-9/control.scm b/module/ice-9/control.scm
index 5f25738..4a114fd 100644
--- a/module/ice-9/control.scm
+++ b/module/ice-9/control.scm
@@ -1,6 +1,6 @@
;;; Beyond call/cc
-;; 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
@@ -21,7 +21,7 @@
(define-module (ice-9 control)
#:re-export (call-with-prompt abort-to-prompt
default-prompt-tag make-prompt-tag)
- #:export (% abort shift reset shift* reset*))
+ #:export (% abort shift reset shift* reset* call/ec let/ec))
(define (abort . args)
(apply abort-to-prompt (default-prompt-tag) args))
@@ -76,3 +76,26 @@
(define (shift* fc)
(shift c (fc c)))
+
+(define %call/ec-prompt
+ (make-prompt-tag))
+
+(define-syntax-rule (call/ec proc)
+ ;; aka. `call-with-escape-continuation'
+ (let ((tag (make-prompt-tag)))
+ (call-with-prompt
+ tag
+ (lambda ()
+ (proc (lambda args (apply abort-to-prompt args))))
+ (lambda (_ . args)
+ (apply values args)))))
+
+(define-syntax-rule (let/ec k e e* ...)
+ ;; aka. `let-escape-continuation'
+ (let ((tag (make-prompt-tag)))
+ (call-with-prompt
+ tag
+ (lambda ()
+ (let ((k (lambda args (apply abort-to-prompt tag args))))
+ e e* ...))
+ (lambda (_ . results) (apply values results)))))
diff --git a/module/ice-9/futures.scm b/module/ice-9/futures.scm
index 35a36ca..90bbe53 100644
--- a/module/ice-9/futures.scm
+++ b/module/ice-9/futures.scm
@@ -23,6 +23,7 @@
#:use-module (srfi srfi-11)
#:use-module (ice-9 q)
#:use-module (ice-9 match)
+ #:use-module (ice-9 control)
#:export (future make-future future? touch))
;;; Author: Ludovic Courtès <l...@gnu.org>
@@ -105,16 +106,6 @@ touched."
(lambda () (begin e0 e1 ...))
(lambda () (unlock-mutex x)))))
-(define-syntax-rule (let/ec k e e* ...) ; TODO: move to core
- (let ((tag (make-prompt-tag)))
- (call-with-prompt
- tag
- (lambda ()
- (let ((k (lambda args (apply abort-to-prompt tag args))))
- e e* ...))
- (lambda (_ res) res))))
-
-
(define %future-prompt
;; The prompt futures abort to when they want to wait for another
;; future.
--
1.7.10.4
