97 lines
3.7 KiB
Scheme
97 lines
3.7 KiB
Scheme
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#!r6rs
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;;; This file is part of SRFI-41: streams
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;;; It is included in Ikarus for your convenience.
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;;; Refer to http://srfi.schemers.org/srfi-41/srfi-41.html for
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;;; details.
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;;;
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;;; Copyright (C) Philip L. Bewig (2007). All Rights Reserved.
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;;; Permission is hereby granted, free of charge, to any person
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;;; obtaining a copy of this software and associated documentation files
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;;; (the "Software"), to deal in the Software without restriction,
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;;; including without limitation the rights to use, copy, modify, merge,
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;;; publish, distribute, sublicense, and/or sell copies of the Software,
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;;; and to permit persons to whom the Software is furnished to do so,
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;;; subject to the following conditions:
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;;;
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;;; The above copyright notice and this permission notice shall be
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;;; included in all copies or substantial portions of the Software.
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;;;
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;;; THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
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;;; EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
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;;; MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
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;;; NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS
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;;; BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN
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;;; ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
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;;; CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
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;;; SOFTWARE.
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(library (streams primitive)
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(export stream-null stream-cons stream? stream-null? stream-pair?
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stream-car stream-cdr stream-lambda)
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(import (rnrs) (rnrs mutable-pairs))
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(define-record-type (stream-type make-stream stream?)
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(fields (mutable box stream-promise stream-promise!)))
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(define-syntax stream-lazy
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(syntax-rules ()
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((lazy expr)
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(make-stream
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(cons 'lazy (lambda () expr))))))
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(define (stream-eager expr)
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(make-stream
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(cons 'eager expr)))
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(define-syntax stream-delay
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(syntax-rules ()
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((stream-delay expr)
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(stream-lazy (stream-eager expr)))))
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(define (stream-force promise)
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(let ((content (stream-promise promise)))
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(case (car content)
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((eager) (cdr content))
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((lazy) (let* ((promise* ((cdr content)))
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(content (stream-promise promise)))
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(if (not (eqv? (car content) 'eager))
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(begin (set-car! content (car (stream-promise promise*)))
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(set-cdr! content (cdr (stream-promise promise*)))
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(stream-promise! promise* content)))
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(stream-force promise))))))
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(define stream-null (stream-delay (cons 'stream 'null)))
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(define-record-type (stream-pare-type make-stream-pare stream-pare?)
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(fields (immutable kar stream-kar) (immutable kdr stream-kdr)))
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(define (stream-pair? obj)
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(and (stream? obj) (stream-pare? (stream-force obj))))
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(define (stream-null? obj)
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(and (stream? obj)
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(eqv? (stream-force obj)
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(stream-force stream-null))))
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(define-syntax stream-cons
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(syntax-rules ()
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((stream-cons obj strm)
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(stream-delay (make-stream-pare (stream-delay obj) (stream-lazy strm))))))
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(define (stream-car strm)
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(cond ((not (stream? strm)) (error 'stream-car "non-stream"))
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((stream-null? strm) (error 'stream-car "null stream"))
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(else (stream-force (stream-kar (stream-force strm))))))
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(define (stream-cdr strm)
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(cond ((not (stream? strm)) (error 'stream-cdr "non-stream"))
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((stream-null? strm) (error 'stream-cdr "null stream"))
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(else (stream-kdr (stream-force strm)))))
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(define-syntax stream-lambda
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(syntax-rules ()
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((stream-lambda formals body0 body1 ...)
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(lambda formals (stream-lazy (let () body0 body1 ...)))))))
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