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|
;;; File: pattern-parser Author: John
;;; This parses the pattern syntax except for the parts which need to be
;;; resolved by precedence parsing.
;;; This parses a list of alternating pats & conops.
(define (parse-pat)
(trace-parser pat
(let ((res (parse-pat/list)))
(if (null? (cdr res))
(car res)
(make pp-pat-list (pats res))))))
;;; This parses a list of patterns with intervening conops and + patterns
(define (parse-pat/list)
(token-case
(con (let ((pcon (pcon->ast)))
(setf (pcon-pats pcon) (parse-apat-list))
(cons pcon (parse-pat/tail))))
(-n
(advance-token) ; past -
(token-case
(numeric (let ((val (literal->ast)))
(cons (make pp-pat-negated)
(cons (make const-pat (value val))
(parse-pat/tail)))))
(else
(signal-missing-token "<number>" "negative literal pattern"))))
(var
(let ((var (var->ast)))
(token-case
(+k (cons (make var-pat (var var))
(parse-+k-pat)))
(@ (let ((pattern (parse-apat)))
(cons (make as-pat (var var) (pattern pattern))
(parse-pat/tail))))
(else (cons (make var-pat (var var)) (parse-pat/tail))))))
(_
(let ((pat (make wildcard-pat)))
(token-case
(+k (cons pat (parse-+k-pat)))
(else (cons pat (parse-pat/tail))))))
(else (let ((apat (parse-apat)))
(cons apat (parse-pat/tail))))))
(define (parse-+k-pat)
(advance-token) ; past +
(token-case
(k (let ((val (literal->ast)))
(cons (make pp-pat-plus)
(cons (make const-pat (value val))
(parse-pat/tail)))))
(else (signal-missing-token "<integer>" "successor pattern"))))
(define (parse-pat/tail)
(token-case
(conop
(let ((con (pconop->ast)))
(cons con (parse-pat/list))))
(else '())))
(define (parse-apat)
(trace-parser apat
(token-case
(var (let ((var (var->ast)))
(token-case
(@
(let ((pattern (parse-apat)))
(make as-pat (var var) (pattern pattern))))
(else (make var-pat (var var))))))
(con (pcon->ast))
(literal (let ((value (literal->ast)))
(make const-pat (value value))))
(_ (make wildcard-pat))
(\( (token-case
(\) (**pcon/def (core-symbol "UnitConstructor") '()))
(else
(let ((pat (parse-pat)))
(token-case
(\, (**pcon/tuple (cons pat (parse-pat-list '\)))))
(\) pat)
(else
(signal-missing-token "`)' or `,'" "pattern")))))))
(\[ (token-case
(\] (make list-pat (pats '())))
(else (make list-pat (pats (parse-pat-list '\]))))))
(\~ (let ((pattern (parse-apat)))
(make irr-pat (pattern pattern))))
(else
(signal-invalid-syntax "an apat")))))
(define (parse-pat-list term) ;; , separated
(let ((pat (parse-pat)))
(token-case
(\, (cons pat (parse-pat-list term)))
((unquote term) (list pat))
(else
(signal-missing-token
(if (eq? term '\)) "`)'" "`]'")
"pattern")))))
(define (parse-apat-list) ;; space separated
(token-case
(apat-start
(let ((pat (parse-apat)))
(cons pat (parse-apat-list))))
(else
'())))
;;; The following routine scans patterns without creating ast structure.
;;; They return #t or #f depending on whether a valid pattern was encountered.
;;; The leave the scanner pointing to the next token after the pattern.
(define (scan-pat) ; same as parse-pat/list
(and
(token-case
(con (scan-con)
(scan-apat-list))
(-n (advance-token)
(token-case
(numeric (advance-token)
'#t)
(else '#f)))
(var (and (scan-var)
(token-case
(@ (scan-apat))
(+k (scan-+k))
(else '#t))))
(_ (scan-+k))
(else (scan-apat)))
(scan-pat/tail)))
(define (scan-pat/tail)
(token-case
(conop (and (scan-conop)
(scan-pat)))
(else '#t)))
(define (scan-apat)
(token-case
(var (scan-var)
(token-case
(@ (scan-apat))
(else '#t)))
(con (scan-con))
(literal (advance-token)
'#t)
(_ '#t)
(\( (token-case
(\) '#t)
(else
(and (scan-pat)
(token-case
(\, (scan-pat-list '\)))
(\) '#t)
(else '#f))))))
(\[ (token-case
(\] '#t)
(else (scan-pat-list '\]))))
(\~ (scan-apat))
(else '#f)))
(define (scan-pat-list term)
(and (scan-pat)
(token-case
(\, (scan-pat-list term))
((unquote term) '#t)
(else '#f))))
(define (scan-apat-list)
(token-case
(apat-start
(and (scan-apat)
(scan-apat-list)))
(else '#t)))
(define (scan-var)
(token-case
(varid '#t)
(\( (token-case
(varsym
(token-case
(\) '#t)
(else '#f)))
(else '#f)))
(else '#f)))
(define (scan-con)
(token-case
(conid '#t)
(\( (token-case
(consym
(token-case
(\) '#t)
(else '#f)))
(else '#f)))
(else '#f)))
(define (scan-conop)
(token-case
(consym '#t)
(\` (token-case
(conid
(token-case
(\` '#t)
(else '#f)))
(else '#f)))
(else '#f)))
(define (scan-+k)
(token-case
(+k (advance-token) ; past the +
(token-case
(integer '#t)
(else '#f)))
(else '#t)))
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