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Linux Cubed Series 7: Sunsite
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population.scm
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1995-10-13
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893b
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38 lines
; Copyright (c) 1993, 1994 Richard Kelsey and Jonathan Rees. See file COPYING.
(define (make-population)
(list '<population>))
(define (add-to-population! x pop)
(if (not x) (error "can't put #f in a population"))
(if (not (weak-memq x (cdr pop)))
(set-cdr! pop (cons (make-weak-pointer x) (cdr pop)))))
(define (weak-memq x weaks)
(if (null? weaks)
#f
(if (eq? x (weak-pointer-ref (car weaks)))
weaks
(weak-memq x (cdr weaks)))))
(define (population-reduce cons nil pop)
(do ((l (cdr pop) (cdr l))
(prev pop l)
(m nil (let ((w (weak-pointer-ref (car l))))
(if w
(cons w m)
(begin (set-cdr! prev (cdr l))
m)))))
((null? l) m)))
(define (population->list pop)
(population-reduce cons '() pop))
(define (walk-population proc pop)
(population-reduce (lambda (thing junk) (proc thing))
#f
pop))