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