ikarus/lib/libcontrol.ss

127 lines
3.1 KiB
Scheme

(let ([winders '()])
(define call-with-current-frame
(lambda (f)
(if ($fp-at-base)
(f ($current-frame))
($seal-frame-and-call f))))
(define primitive-call/cc
(lambda (f)
(call-with-current-frame
(lambda (frm)
(f ($frame->continuation frm))))))
(define len
(lambda (ls n)
(if (null? ls)
n
(len (cdr ls) (fxadd1 n)))))
(define list-tail
(lambda (ls n)
(if (fxzero? n)
ls
(list-tail (cdr ls) (fxsub1 n)))))
(define drop-uncommon-heads
(lambda (x y)
(if (eq? x y)
x
(drop-uncommon-heads (cdr x) (cdr y)))))
(define common-tail
(lambda (x y)
(let ([lx (len x 0)] [ly (len y 0)])
(let ([x (if (fx> lx ly) (list-tail x (fx- lx ly)) x)]
[y (if (fx> ly lx) (list-tail y (fx- ly lx)) y)])
(if (eq? x y)
x
(drop-uncommon-heads (cdr x) (cdr y)))))))
(define unwind*
(lambda (ls tail)
(unless (eq? ls tail)
(set! winders (cdr ls))
((cdar ls))
(unwind* (cdr ls) tail))))
(define rewind*
(lambda (ls tail)
(unless (eq? ls tail)
(rewind* (cdr ls) tail)
((caar ls))
(set! winders ls))))
(define do-wind
(lambda (new)
(let ([tail (common-tail new winders)])
(unwind* winders tail)
(rewind* new tail))))
;;; (define call/cc
;;; (lambda (f)
;;; (primitive-call/cc
;;; (lambda (k)
;;; (let ([save winders])
;;; (f (lambda v*
;;; (unless (eq? save winders) (do-wind save))
;;; (apply k v*))))))))
(define call/cc
(lambda (f)
(primitive-call/cc
(lambda (k)
(let ([save winders])
(f (case-lambda
[(v) (unless (eq? save winders) (do-wind save)) (k v)]
[() (unless (eq? save winders) (do-wind save)) (k)]
[(v1 v2 . v*)
(unless (eq? save winders) (do-wind save))
(apply k v1 v2 v*)])))))))
;;; (define dynamic-wind
;;; (lambda (in body out)
;;; (in)
;;; (set! winders (cons (cons in out) winders))
;;; (let ([v (body)])
;;; (set! winders (cdr winders))
;;; (out)
;;; v)))
;;; (define dynamic-wind
;;; (lambda (in body out)
;;; (in)
;;; (set! winders (cons (cons in out) winders))
;;; (call-with-values
;;; body
;;; (lambda v*
;;; (set! winders (cdr winders))
;;; (out)
;;; (apply values v*)))))
(define dynamic-wind
(lambda (in body out)
(in)
(set! winders (cons (cons in out) winders))
(call-with-values
body
(case-lambda
[(v) (set! winders (cdr winders)) (out) v]
[() (set! winders (cdr winders)) (out) (values)]
[(v1 v2 . v*)
(set! winders (cdr winders))
(out)
(apply values v1 v2 v*)]))))
(primitive-set! 'call/cf call-with-current-frame)
(primitive-set! 'call/cc call/cc)
(primitive-set! 'dynamic-wind dynamic-wind)
(void))