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(define-library (csc match)
(export match)
(import (scheme base))
(begin
(define-record-type <no-match>
(make-no-match)
no-match?)
(define-syntax match-pattern
(syntax-rules (_ ! when)
((match-pattern x pattern (when condition) result result* ...)
(match-pattern x pattern
(if condition
(begin result result* ...)
(raise (make-no-match)))))
((match-pattern x _ result result* ...)
(begin result result* ...))
((match-pattern x '() result result* ...)
(if (null? x)
(begin result result* ...)
(raise (make-no-match))))
((match-pattern x (! constant) result result* ...)
(if (equal? x constant)
(begin result result* ...)
(raise (make-no-match))))
((match-pattern x (pattern) result result* ...)
(let ((y x))
(if (= 1 (length y))
(match-pattern (car y) pattern result result* ...)
(raise (make-no-match)))))
((match-pattern x (pattern . rest) result result* ...)
(let ((y x))
(if (pair? y)
(match-pattern (car y) pattern
(match-pattern (cdr y) rest result result* ...))
(raise (make-no-match)))))
((match-pattern x identifier result result* ...)
(let ((identifier x))
result result* ...))))
(define-syntax match
(syntax-rules ()
((match x (arm ...))
(guard (e ((no-match? e) (if #f #f)))
(match-pattern x arm ...)))
((match x (arm ...) clause clause* ...)
(let ((y x))
(guard (e ((no-match? e)
(match y clause clause* ...)))
(match-pattern y arm ...))))))))
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