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(define-module (language scheme amatch)
#:use-module (ice-9 syncase)
#:export (amatch apat))
;; FIXME: shouldn't have to export apat...
;; This is exactly the same as pmatch except that it unpacks annotations
;; as needed.
(define-syntax amatch
(syntax-rules (else guard)
((_ (op arg ...) cs ...)
(let ((v (op arg ...)))
(amatch v cs ...)))
((_ v) (if #f #f))
((_ v (else e0 e ...)) (begin e0 e ...))
((_ v (pat (guard g ...) e0 e ...) cs ...)
(let ((fk (lambda () (amatch v cs ...))))
(apat v pat
(if (and g ...) (begin e0 e ...) (fk))
(fk))))
((_ v (pat e0 e ...) cs ...)
(let ((fk (lambda () (amatch v cs ...))))
(apat v pat (begin e0 e ...) (fk))))))
(define-syntax apat
(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 (apair? v)
(let ((vx (acar v)) (vy (acdr v)))
(apat vx x (apat vy y kt kf) kf))
kf))
((_ v lit kt kf) (if (eq? v (quote lit)) kt kf))))
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