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35 lines
1.1 KiB
Scheme
35 lines
1.1 KiB
Scheme
(define-module (language scheme amatch)
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#:export (amatch))
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;; This is exactly the same as pmatch except that it unpacks annotations
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;; as needed.
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(define-syntax amatch
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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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(amatch 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 () (amatch v cs ...))))
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(apat 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 () (amatch v cs ...))))
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(apat v pat (begin e0 e ...) (fk))))))
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(define-syntax apat
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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 (apair? v)
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(let ((vx (acar v)) (vy (acdr v)))
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(apat vx x (apat 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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