FM / srfi

/usr/share/guile/2.0/srfi

Name	Size	Mode	Actions
srfi-4/	-	0755	rm
srfi-9/	-	0755	rm
srfi-42/	-	0755	rm
srfi-64/	-	0755	rm
srfi-67/	-	0755	rm
srfi-1.scm	29091	0644	edit dl rm
srfi-2.scm	1105	0644	edit dl rm
srfi-4.scm	5107	0644	edit dl rm
srfi-6.scm	1594	0644	edit dl rm
srfi-8.scm	1103	0644	edit dl rm
srfi-9.scm	13429	0644	edit dl rm
srfi-10.scm	2830	0644	edit dl rm
srfi-11.scm	5511	0644	edit dl rm
srfi-13.scm	2788	0644	edit dl rm
srfi-14.scm	2386	0644	edit dl rm
srfi-16.scm	1883	0644	edit dl rm
srfi-17.scm	6573	0644	edit dl rm
srfi-18.scm	12198	0644	edit dl rm
srfi-19.scm	57263	0644	edit dl rm
srfi-26.scm	2643	0644	edit dl rm
srfi-27.scm	3051	0644	edit dl rm
srfi-28.scm	1193	0644	edit dl rm
srfi-31.scm	1395	0644	edit dl rm
srfi-34.scm	3276	0644	edit dl rm
srfi-35.scm	12269	0644	edit dl rm
srfi-37.scm	8566	0644	edit dl rm
srfi-38.scm	8387	0644	edit dl rm
srfi-39.scm	2159	0644	edit dl rm
srfi-41.scm	20390	0644	edit dl rm
srfi-42.scm	1796	0644	edit dl rm
srfi-43.scm	40005	0644	edit dl rm
srfi-45.scm	3583	0644	edit dl rm
srfi-60.scm	2174	0644	edit dl rm
srfi-64.scm	2571	0644	edit dl rm
srfi-67.scm	2362	0644	edit dl rm
srfi-69.scm	13001	0644	edit dl rm
srfi-88.scm	1755	0644	edit dl rm
srfi-98.scm	1612	0644	edit dl rm
srfi-111.scm	1313	0644	edit dl rm

Edit: /usr/share/guile/2.0/srfi/srfi-45.scm (3583B)

;;; srfi-45.scm -- Primitives for Expressing Iterative Lazy Algorithms

;; Permission is hereby granted, free of charge, to any person
;; obtaining a copy of this software and associated documentation
;; files (the "Software"), to deal in the Software without
;; restriction, including without limitation the rights to use, copy,
;; modify, merge, publish, distribute, sublicense, and/or sell copies
;; of the Software, and to permit persons to whom the Software is
;; furnished to do so, subject to the following conditions:

;; The above copyright notice and this permission notice shall be
;; included in all copies or substantial portions of the Software.

;; THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
;; EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
;; MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
;; NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS
;; BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN
;; ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
;; CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
;; SOFTWARE.

;;; Commentary:

;; This is the code of the reference implementation of SRFI-45, modified
;; to use SRFI-9 and to add 'promise?' to the list of exports.

;; This module is documented in the Guile Reference Manual.

;;; Code:

(define-module (srfi srfi-45)
  #:export (delay
             lazy
             force
             eager
             promise?)
  #:replace (delay force promise?)
  #:use-module (srfi srfi-9)
  #:use-module (srfi srfi-9 gnu))

(cond-expand-provide (current-module) '(srfi-45))

(define-record-type promise (make-promise val) promise?
  (val promise-val promise-val-set!))

(define-record-type value (make-value tag proc) value?
  (tag value-tag value-tag-set!)
  (proc value-proc value-proc-set!))

(define-syntax-rule (lazy exp)
  (make-promise (make-value 'lazy (lambda () exp))))

(define (eager x)
  (make-promise (make-value 'eager x)))

(define-syntax-rule (delay exp)
  (lazy (eager exp)))

(define (force promise)
  (let ((content (promise-val promise)))
    (case (value-tag content)
      ((eager) (value-proc content))
      ((lazy)  (let* ((promise* ((value-proc content)))
                      (content  (promise-val promise)))        ; *
                 (if (not (eqv? (value-tag content) 'eager))   ; *
                     (begin (value-tag-set! content
                                            (value-tag (promise-val promise*)))
                            (value-proc-set! content
                                             (value-proc (promise-val promise*)))
                            (promise-val-set! promise* content)))
                 (force promise))))))

;; (*) These two lines re-fetch and check the original promise in case
;;     the first line of the let* caused it to be forced.  For an example
;;     where this happens, see reentrancy test 3 below.

(define* (promise-visit promise #:key on-eager on-lazy)
  (define content (promise-val promise))
  (case (value-tag content)
    ((eager) (on-eager (value-proc content)))
    ((lazy)  (on-lazy (value-proc content)))))

(set-record-type-printer! promise
  (lambda (promise port)
    (promise-visit promise
      #:on-eager (lambda (value)
                   (format port "#<promise = ~s>" value))
      #:on-lazy  (lambda (proc)
                   (format port "#<promise => ~s>" proc)))))

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