srfi-39 implementation -- Bug fix

;;; srfi-39.scm --- Parameter objects

;; 	Copyright (C) 2004 Free Software Foundation, Inc.
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;;; Author: Jose Antonio Ortega Ruiz <[email protected]>
;;; 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*))

(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))


; arch-tag: 536b6766-9947-4ad0-a35e-2420000d8a72

(use-modules (srfi srfi-39))


(define (check a b a-val b-val)
  (if (not (eqv? (a) a-val)) (error "failure -- a" (a) a-val))
  (if (not (eqv? (b) b-val)) (error "failure -- b" (b) b-val)))

(define a (make-parameter 3))
(define b (make-parameter 4))

(check a b 3 4)

(parameterize ((a 2) (b 1))
  (check a b 2 1)
  (parameterize ((b 8))
    (check a b 2 8)))

(check a b 3 4)

(define c (make-parameter 2 (lambda (x) (if (< x 10) x 10))))
(define d (make-parameter 15 (lambda (x) (if (< x 10) x 10))))

(check c d 2 10)

(parameterize ((a 0) (b 1) (c 98) (d 9))
  (check a b 0 1)
  (check c d 10 9)
  (parameterize ((c (a)) (d (b)))
    (check a b 0 1)
    (check c d 0 1)))