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(define-library (csc match)
(export
define-match-record-type
match)
(import (scheme base))
(begin
(define-record-type <no-match>
(make-no-match)
no-match?)
(define *no-match* (make-no-match))
(define-syntax define-match-record-type
(syntax-rules ()
((define-match-record-type name constructor predicate matcher (field-name* field-getter*) ...)
(begin
(define-record-type name
constructor
predicate
(field-name* field-getter*) ...)
(define (matcher x)
(unless (predicate x)
(raise *no-match*))
(list (cons '!type 'name) (cons 'field-name* (field-getter* x)) ...))))))
(define-syntax match-pattern
(syntax-rules (% _ quote when)
((match-pattern x pattern when condition result result* ...)
(match-pattern x pattern
(unless condition
(raise *no-match*))
result result* ...))
((match-pattern x _ result result* ...)
(let () result result* ...))
((match-pattern x (quote constant) result result* ...)
(let ()
(unless (equal? x (quote constant))
(raise *no-match*))
result result* ...))
((match-pattern x (% record-matcher) result result* ...)
(let ()
(record-matcher x)
result result* ...))
((match-pattern x (% record-matcher . patterns) result result* ...)
(let ((x* (record-matcher x)))
(match-pattern (map cdr (cdr x*)) patterns result result* ...)))
((match-pattern x () result* ...)
(syntax-error "Unexpected pattern (). Use '() to match nil."))
((match-pattern x (pattern) result result* ...)
(let ((y x))
(unless (and (pair? y)
(null? (cdr y)))
(raise *no-match*))
(match-pattern (car y) pattern result result* ...)))
((match-pattern x (pattern . rest) result result* ...)
(let ((y x))
(unless (pair? y)
(raise *no-match*))
(match-pattern (car y) pattern
(match-pattern (cdr y) rest result result* ...))))
((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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