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authorMarius Vollmer <mvo@zagadka.de>2004-08-15 20:26:05 +0000
committerMarius Vollmer <mvo@zagadka.de>2004-08-15 20:26:05 +0000
commit3514320f60c5c77716691055c8e2a6eeae7681e6 (patch)
tree99f937a32bc836b7a94c13da3b688ca349c81d1f /srfi/srfi-39.scm
parent80b707b7541e84db6533907fed31efa2dd264ca3 (diff)
downloadguile-3514320f60c5c77716691055c8e2a6eeae7681e6.tar.gz
New, from Jose A Ortega Ruiz. Thanks!
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+;;; srfi-39.scm --- Parameter objects
+
+;; Copyright (C) 2004 Free Software Foundation, Inc.
+;;
+;; This program is free software; you can redistribute it and/or
+;; modify it under the terms of the GNU General Public License as
+;; published by the Free Software Foundation; either version 2, or
+;; (at your option) any later version.
+;;
+;; This program is distributed in the hope that it will be useful,
+;; but WITHOUT ANY WARRANTY; without even the implied warranty of
+;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
+;; General Public License for more details.
+;;
+;; You should have received a copy of the GNU General Public License
+;; along with this software; see the file COPYING. If not, write to
+;; the Free Software Foundation, Inc., 59 Temple Place, Suite 330,
+;; Boston, MA 02111-1307 USA
+;;
+;; As a special exception, the Free Software Foundation gives permission
+;; for additional uses of the text contained in its release of GUILE.
+;;
+;; The exception is that, if you link the GUILE library with other files
+;; to produce an executable, this does not by itself cause the
+;; resulting executable to be covered by the GNU General Public License.
+;; Your use of that executable is in no way restricted on account of
+;; linking the GUILE library code into it.
+;;
+;; This exception does not however invalidate any other reasons why
+;; the executable file might be covered by the GNU General Public License.
+;;
+;; This exception applies only to the code released by the
+;; Free Software Foundation under the name GUILE. If you copy
+;; code from other Free Software Foundation releases into a copy of
+;; GUILE, as the General Public License permits, the exception does
+;; not apply to the code that you add in this way. To avoid misleading
+;; anyone as to the status of such modified files, you must delete
+;; this exception notice from them.
+;;
+;; If you write modifications of your own for GUILE, it is your choice
+;; whether to permit this exception to apply to your modifications.
+;; If you do not wish that, delete this exception notice.
+
+;;; Author: Jose Antonio Ortega Ruiz <jao@gnu.org>
+;;; Date: 2004-05-05
+
+;;; Commentary:
+
+;; This is an implementation of SRFI-39 (Parameter objects).
+;;
+;; The implementation is based on Guile's fluid objects, and is, therefore,
+;; thread-safe (parameters are thread-local).
+;;
+;; In addition to the forms defined in SRFI-39 (`make-parameter',
+;; `parameterize'), a new procedure `with-parameters*' is provided.
+;; This procedures is analogous to `with-fluids*' but taking as first
+;; argument a list of parameter objects instead of a list of fluids.
+;;
+
+;;; Code:
+
+(define-module (srfi srfi-39)
+ #:use-module (ice-9 syncase)
+ #:use-module (srfi srfi-16)
+
+ #:export (make-parameter)
+ #:export-syntax (parameterize)
+
+ ;; helper procedure not in srfi-39.
+ #:export (with-parameters*))
+
+;; Make 'srfi-39 available as a feature identifiere to `cond-expand'.
+;;
+(cond-expand-provide (current-module) '(srfi-39))
+
+(define make-parameter
+ (case-lambda
+ ((val) (make-parameter/helper val (lambda (x) x)))
+ ((val conv) (make-parameter/helper val conv))))
+
+(define get-fluid-tag (lambda () 'get-fluid)) ;; arbitrary unique (as per eq?) value
+(define get-conv-tag (lambda () 'get-conv)) ;; arbitrary unique (as per eq?) value
+
+(define (make-parameter/helper val conv)
+ (let ((value (make-fluid))
+ (conv conv))
+ (begin
+ (fluid-set! value (conv val))
+ (lambda new-value
+ (cond
+ ((null? new-value) (fluid-ref value))
+ ((eq? (car new-value) get-fluid-tag) value)
+ ((eq? (car new-value) get-conv-tag) conv)
+ ((null? (cdr new-value)) (fluid-set! value (conv (car new-value))))
+ (else (error "make-parameter expects 0 or 1 arguments" new-value)))))))
+
+(define-syntax parameterize
+ (syntax-rules ()
+ ((_ ((?param ?value) ...) ?body ...)
+ (with-parameters* (list ?param ...)
+ (list ?value ...)
+ (lambda () ?body ...)))))
+
+(define (with-parameters* params values thunk)
+ (with-fluids* (map (lambda (p) (p get-fluid-tag)) params)
+ (map (lambda (p v) ((p get-conv-tag) v)) params values)
+ thunk))