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srfi/srfi-39.scm

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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))

test-suite/tests/srfi-39.test

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+;;;; srfi-39.test --- -*- scheme -*-
+;;;;
+;;;; 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
+
+(use-modules (srfi srfi-39))
+
+(define a (make-parameter 3))
+(define b (make-parameter 4))
+
+(define (check a b a-val b-val)
+  (and (eqv? (a) a-val)) (eqv? (b) b-val))
+
+(define c (make-parameter 2 (lambda (x) (if (< x 10) x 10))))
+(define d (make-parameter 15 (lambda (x) (if (< x 10) x 10))))
+
+(with-test-prefix "SRFI-39"
+
+  (pass-if "test 1"
+    (check a b 3 4))
+
+  (pass-if "test 2"
+    (parameterize ((a 2) (b 1))
+      (and (check a b 2 1)
+	   (parameterize ((b 8))
+	     (check a b 2 8)))))
+
+  (pass-if "test 3"
+    (check a b 3 4))
+
+  (pass-if "test 4"
+    (check c d 2 10))
+
+  (pass-if "test 5"
+    (parameterize ((a 0) (b 1) (c 98) (d 9))
+      (and (check a b 0 1)
+           (check c d 10 9)
+           (parameterize ((c (a)) (d (b)))
+	     (and (check a b 0 1)
+		  (check c d 0 1)))))))