Created
May 6, 2019 01:10
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;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;; | |
(define (assert pred) | |
(or pred (amb))) | |
(define amb-queue (make-parameter #f)) | |
(define amb-escape (make-parameter #f)) | |
(define-syntax-rule (begin-amb fail body ...) | |
(let/cc k | |
(parameterize ([amb-queue '()] | |
[amb-escape (λ () (k fail))]) | |
body ...))) | |
(define-syntax-rule (amb alt ...) | |
(let/cc k | |
(amb-queue (append (amb-queue) | |
(list (λ () (k alt)) ...))) | |
(if (empty? (amb-queue)) | |
((amb-escape)) | |
(let ([top (car (amb-queue))]) | |
(amb-queue (cdr (amb-queue))) | |
(top))))) | |
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;; | |
(define (ε k) k) | |
(define (((char c) k) u) | |
(assert (and (cons? u) (eq? (car u) c))) | |
(k (cdr u))) | |
(define ((alt p q) k) | |
((amb p q) k)) | |
(define ((seq p q) k) | |
(p (q k))) | |
(define (((rep r) k) u) | |
((amb k (r ((rep r) k))) u)) | |
(define (accept? r u) | |
(begin-amb #f ((r (λ (u) (assert (empty? u)))) u))) | |
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;; | |
(define (str s) | |
(for/fold ([f ε]) | |
([c (string->list s)]) | |
(seq f (char c)))) | |
(accept? (alt (str "hi") (str "there")) | |
(string->list "hi")) | |
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;; |
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