49 lines
1.4 KiB
Scheme
49 lines
1.4 KiB
Scheme
;;; Portd from Scheme 48 1.9. See file COPYING for notices and license.
|
|
;;;
|
|
;;; Port Author: Andrew Whatson
|
|
;;;
|
|
;;; Original Authors: Richard Kelsey, Jonathan Rees
|
|
|
|
(define-module (prescheme population)
|
|
#:use-module (prescheme scheme48)
|
|
#:export (make-population
|
|
add-to-population!
|
|
population->list
|
|
walk-population))
|
|
|
|
(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))
|
|
|
|
;; FIXME: do we *actually* need weak refs?
|
|
(define (make-weak-pointer x) x)
|
|
(define (weak-pointer-ref x) x)
|