diff options
Diffstat (limited to 'module/srfi/srfi-39.scm')
-rw-r--r-- | module/srfi/srfi-39.scm | 137 |
1 files changed, 137 insertions, 0 deletions
diff --git a/module/srfi/srfi-39.scm b/module/srfi/srfi-39.scm new file mode 100644 index 000000000..086751170 --- /dev/null +++ b/module/srfi/srfi-39.scm @@ -0,0 +1,137 @@ +;;; srfi-39.scm --- Parameter objects + +;; Copyright (C) 2004, 2005, 2006, 2008 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 +;; License as published by the Free Software Foundation; either +;; version 2.1 of the License, or (at your option) any later version. +;; +;; This library 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 +;; Lesser General Public License for more details. +;; +;; You should have received a copy of the GNU Lesser General Public +;; License along with this library; if not, write to the Free Software +;; Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA + +;;; 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*) + #:replace (current-input-port current-output-port current-error-port)) + +;; 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 (current-input-port . new-value) + (if (null? new-value) + ((@ (guile) current-input-port)) + (apply set-current-input-port new-value))) + +(define (current-output-port . new-value) + (if (null? new-value) + ((@ (guile) current-output-port)) + (apply set-current-output-port new-value))) + +(define (current-error-port . new-value) + (if (null? new-value) + ((@ (guile) current-error-port)) + (apply set-current-error-port new-value))) + +(define port-list + (list current-input-port current-output-port current-error-port)) + +;; There are no fluids behind current-input-port etc, so those parameter +;; objects are picked out of the list and handled separately with a +;; dynamic-wind to swap their values to and from a location (the "value" +;; variable in the swapper procedure "let"). +;; +;; current-input-port etc are already per-dynamic-root, so this arrangement +;; works the same as a fluid. Perhaps they could become fluids for ease of +;; implementation here. +;; +;; Notice the use of a param local variable for the swapper procedure. It +;; ensures any application changes to the PARAMS list won't affect the +;; winding. +;; +(define (with-parameters* params values thunk) + (let more ((params params) + (values values) + (fluids '()) ;; fluids from each of PARAMS + (convs '()) ;; VALUES with conversion proc applied + (swapper noop)) ;; wind/unwind procedure for ports handling + (if (null? params) + (if (eq? noop swapper) + (with-fluids* fluids convs thunk) + (dynamic-wind + swapper + (lambda () + (with-fluids* fluids convs thunk)) + swapper)) + (if (memq (car params) port-list) + (more (cdr params) (cdr values) + fluids convs + (let ((param (car params)) + (value (car values)) + (prev-swapper swapper)) + (lambda () + (set! value (param value)) + (prev-swapper)))) + (more (cdr params) (cdr values) + (cons ((car params) get-fluid-tag) fluids) + (cons (((car params) get-conv-tag) (car values)) convs) + swapper))))) |