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(define-module (system base pmatch)
#:export (pmatch))
;; FIXME: shouldn't have to export ppat...
;; Originally written by Oleg Kiselyov. Taken from:
;; αKanren: A Fresh Name in Nominal Logic Programming
;; by William E. Byrd and Daniel P. Friedman
;; Proceedings of the 2007 Workshop on Scheme and Functional Programming
;; Université Laval Technical Report DIUL-RT-0701
;; Licensing unclear. Probably need to ask Oleg for a disclaimer.
(define-syntax pmatch
(syntax-rules (else guard)
((_ (op arg ...) cs ...)
(let ((v (op arg ...)))
(pmatch v cs ...)))
((_ v) (if #f #f))
((_ v (else e0 e ...)) (let () e0 e ...))
((_ v (pat (guard g ...) e0 e ...) cs ...)
(let ((fk (lambda () (pmatch v cs ...))))
(ppat v pat
(if (and g ...) (let () e0 e ...) (fk))
(fk))))
((_ v (pat e0 e ...) cs ...)
(let ((fk (lambda () (pmatch v cs ...))))
(ppat v pat (let () e0 e ...) (fk))))))
(define-syntax ppat
(syntax-rules (_ quote unquote)
((_ v _ kt kf) kt)
((_ v () kt kf) (if (null? v) kt kf))
((_ v (quote lit) kt kf)
(if (equal? v (quote lit)) kt kf))
((_ v (unquote var) kt kf) (let ((var v)) kt))
((_ v (x . y) kt kf)
(if (pair? v)
(let ((vx (car v)) (vy (cdr v)))
(ppat vx x (ppat vy y kt kf) kf))
kf))
((_ v lit kt kf) (if (eq? v (quote lit)) kt kf))))
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