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; Part of Scheme 48 1.9. See file COPYING for notices and license.
; Authors: Richard Kelsey, Jonathan Rees
(define (make-population)
(list '<population>))
(define (add-to-population! x pop)
(if (not x) (assertion-violation 'add-to-population! "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))
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