ikarus/lib/streams/primitive.ss

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#!r6rs
;;; This file is part of SRFI-41: streams
;;; It is included in Ikarus for your convenience.
;;; Refer to http://srfi.schemers.org/srfi-41/srfi-41.html for
;;; details.
;;;
;;; Copyright (C) Philip L. Bewig (2007). All Rights Reserved.
;;; 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.
(library (streams primitive)
(export stream-null stream-cons stream? stream-null? stream-pair?
stream-car stream-cdr stream-lambda)
(import (rnrs) (rnrs mutable-pairs))
(define-record-type (stream-type make-stream stream?)
(fields (mutable box stream-promise stream-promise!)))
(define-syntax stream-lazy
(syntax-rules ()
((lazy expr)
(make-stream
(cons 'lazy (lambda () expr))))))
(define (stream-eager expr)
(make-stream
(cons 'eager expr)))
(define-syntax stream-delay
(syntax-rules ()
((stream-delay expr)
(stream-lazy (stream-eager expr)))))
(define (stream-force promise)
(let ((content (stream-promise promise)))
(case (car content)
((eager) (cdr content))
((lazy) (let* ((promise* ((cdr content)))
(content (stream-promise promise)))
(if (not (eqv? (car content) 'eager))
(begin (set-car! content (car (stream-promise promise*)))
(set-cdr! content (cdr (stream-promise promise*)))
(stream-promise! promise* content)))
(stream-force promise))))))
(define stream-null (stream-delay (cons 'stream 'null)))
(define-record-type (stream-pare-type make-stream-pare stream-pare?)
(fields (immutable kar stream-kar) (immutable kdr stream-kdr)))
(define (stream-pair? obj)
(and (stream? obj) (stream-pare? (stream-force obj))))
(define (stream-null? obj)
(and (stream? obj)
(eqv? (stream-force obj)
(stream-force stream-null))))
(define-syntax stream-cons
(syntax-rules ()
((stream-cons obj strm)
(stream-delay (make-stream-pare (stream-delay obj) (stream-lazy strm))))))
(define (stream-car strm)
(cond ((not (stream? strm)) (error 'stream-car "non-stream"))
((stream-null? strm) (error 'stream-car "null stream"))
(else (stream-force (stream-kar (stream-force strm))))))
(define (stream-cdr strm)
(cond ((not (stream? strm)) (error 'stream-cdr "non-stream"))
((stream-null? strm) (error 'stream-cdr "null stream"))
(else (stream-kdr (stream-force strm)))))
(define-syntax stream-lambda
(syntax-rules ()
((stream-lambda formals body0 body1 ...)
(lambda formals (stream-lazy (let () body0 body1 ...)))))))