module/srfi/srfi-39.scm

   1 ;;; srfi-39.scm --- Parameter objects
   2
   3 ;;      Copyright (C) 2004, 2005, 2006, 2008, 2011 Free Software Foundation, Inc.
   4 ;;
   5 ;; This library is free software; you can redistribute it and/or
   6 ;; modify it under the terms of the GNU Lesser General Public
   7 ;; License as published by the Free Software Foundation; either
   8 ;; version 3 of the License, or (at your option) any later version.
   9 ;;
  10 ;; This library is distributed in the hope that it will be useful,
  11 ;; but WITHOUT ANY WARRANTY; without even the implied warranty of
  12 ;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  13 ;; Lesser General Public License for more details.
  14 ;;
  15 ;; You should have received a copy of the GNU Lesser General Public
  16 ;; License along with this library; if not, write to the Free Software
  17 ;; Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
  18
  19 ;;; Author: Jose Antonio Ortega Ruiz <jao@gnu.org>
  20 ;;; Date: 2004-05-05
  21
  22 ;;; Commentary:
  23
  24 ;; This is an implementation of SRFI-39 (Parameter objects).
  25 ;;
  26 ;; The implementation is based on Guile's fluid objects, and is, therefore,
  27 ;; thread-safe (parameters are thread-local).
  28 ;;
  29 ;; In addition to the forms defined in SRFI-39 (`make-parameter',
  30 ;; `parameterize'), a new procedure `with-parameters*' is provided.
  31 ;; This procedures is analogous to `with-fluids*' but taking as first
  32 ;; argument a list of parameter objects instead of a list of fluids.
  33 ;;
  34
  35 ;;; Code:
  36
  37 (define-module (srfi srfi-39)
  38   ;; helper procedure not in srfi-39.
  39   #:export (with-parameters*)
  40   #:re-export (make-parameter
  41                parameterize
  42                current-input-port current-output-port current-error-port))
  43
  44 (cond-expand-provide (current-module) '(srfi-39))
  45
  46 (define (with-parameters* params values thunk)
  47   (let more ((params params)
  48              (values values)
  49              (fluids '())     ;; fluids from each of PARAMS
  50              (convs  '()))    ;; VALUES with conversion proc applied
  51     (if (null? params)
  52         (with-fluids* fluids convs thunk)
  53         (more (cdr params) (cdr values)
  54               (cons (parameter-fluid (car params)) fluids)
  55               (cons ((parameter-converter (car params)) (car values)) convs)))))