50 lines
1.4 KiB
Scheme
50 lines
1.4 KiB
Scheme
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;;; Portd from Scheme 48 1.9. See file COPYING for notices and license.
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;;;
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;;; Port Author: Andrew Whatson
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;;;
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;;; Original Authors: Richard Kelsey, Jonathan Rees
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(define-module (prescheme population)
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#:use-module (prescheme scheme48)
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#:export (make-population
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add-to-population!
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population->list
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walk-population))
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(define (make-population)
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(list '<population>))
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(define (add-to-population! x pop)
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(if (not x) (assertion-violation 'add-to-population! "can't put #f in a population"))
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(if (not (weak-memq x (cdr pop)))
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(set-cdr! pop (cons (make-weak-pointer x) (cdr pop)))))
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(define (weak-memq x weaks)
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(if (null? weaks)
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#f
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(if (eq? x (weak-pointer-ref (car weaks)))
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weaks
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(weak-memq x (cdr weaks)))))
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(define (population-reduce cons nil pop)
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(do ((l (cdr pop) (cdr l))
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(prev pop l)
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(m nil (let ((w (weak-pointer-ref (car l))))
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(if w
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(cons w m)
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(begin (set-cdr! prev (cdr l))
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m)))))
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((null? l) m)))
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(define (population->list pop)
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(population-reduce cons '() pop))
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(define (walk-population proc pop)
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(population-reduce (lambda (thing junk) (proc thing))
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#f
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pop))
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;; FIXME: do we *actually* need weak refs?
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(define (make-weak-pointer x) x)
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(define (weak-pointer-ref x) x)
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