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br-parser-tools/collects/parser-tools/lex.ss

200 lines
5.7 KiB
Scheme

(module lex mzscheme
;; Provides the syntax used to create lexers and the functions needed to
;; create and use the buffer that the lexer reads from. See doc.txt.
(require-for-syntax "private-lex/generate-code.ss")
(require-for-syntax "private-lex/structs.ss")
(require (lib "list.ss"))
(provide lex define-lex-abbrev define-lex-abbrevs
make-lex-buf
get-position position-offset position-line position-col position?)
(define-syntax lex
(let ((code
`(letrec ((match
(lambda (lb first-pos longest-match-length longest-match-action length)
(let ((match
(push-back lb (- length longest-match-length))))
(if (not longest-match-action)
(error 'lex "No match found in rest of input"))
(longest-match-action
(lambda ()
first-pos)
(lambda ()
(get-position lb))
(lambda ()
(list->string (reverse (filter (lambda (x)
(char? x))
match))))
lb)))))
(lambda (lb)
(unless (lex-buffer? lb)
(error 'lex
(format
"Lexer expects argument of type lex-buf; given ~a" lb)))
(let ((first-pos (get-position lb)))
(let loop (
;; current-state
(state start-state)
;; the character to transition on
(char (next-char lb))
;; action for the longest match seen thus far
;; including a match at the current state
(longest-match-action
(vector-ref actions start-state))
;; how many characters have been read
;; including the one just read
(length 1)
;; how many characters are in the longest match
(longest-match-length 0))
(let ((next-state
(cond
((eof-object? char)
(vector-ref eof-table state))
(else
(vector-ref
trans-table
(bitwise-ior (char->integer char)
(arithmetic-shift state 8)))))))
(cond
((not next-state) (match lb
first-pos
longest-match-length
longest-match-action
length))
(else
(loop next-state
(next-char lb)
(if (vector-ref actions next-state)
(vector-ref actions next-state)
longest-match-action)
(add1 length)
(if (vector-ref actions next-state)
length
longest-match-length)))))))))))
(lambda (stx)
(syntax-case stx ()
((_ (re act) ...)
(let* ((table (generate-table (syntax ((re act) ...))
stx))
(code
`(let ((start-state ,(table-start table))
(trans-table ,(table-trans table))
(eof-table ,(table-eof table))
(actions (vector ,@(vector->list (table-actions table)))))
,code)))
(datum->syntax-object #'here code #f)))))))
(define-syntax define-lex-abbrev
(syntax-rules ()
((_ name val) (define-syntax name
(make-lex-abbrev (quote-syntax val))))))
(define-syntax define-lex-abbrevs
(syntax-rules ()
((_ (name val) ...)
(define-syntaxes (name ...)
(values (make-lex-abbrev (quote-syntax val)) ...)))))
;; Lex buffer is NOT thread safe
;; c = char | eof
;; lex-buf =
;; (make-lex-buffer input-port (c list) (c list) int int int (int list))
(define-struct lex-buffer (ip from to offset line col line-lengths))
;; make-lex-buf: input-port -> lex-buf
(define (make-lex-buf ip)
(make-lex-buffer ip null null 0 0 0 null))
;; next-char: lex-buf -> c
;; gets the next character from the buffer
(define (next-char lb)
(let ((char-in
(cond
((null? (lex-buffer-from lb))
(read-char (lex-buffer-ip lb)))
(else (begin0
(car (lex-buffer-from lb))
(set-lex-buffer-from! lb (cdr (lex-buffer-from lb))))))))
(set-lex-buffer-to! lb (cons char-in (lex-buffer-to lb)))
(cond
((eq? #\newline char-in)
(set-lex-buffer-line-lengths!
lb
(cons (lex-buffer-col lb)
(lex-buffer-line-lengths lb)))
(set-lex-buffer-line! lb (add1 (lex-buffer-line lb)))
(set-lex-buffer-col! lb 0))
(else
(set-lex-buffer-col! lb (add1 (lex-buffer-col lb)))))
(set-lex-buffer-offset! lb (add1 (lex-buffer-offset lb)))
char-in))
;; push-back: lex-buf * int -> c list
;; pushes the last read i characters back to be read again
;; returns the characters not pushed back and read after the last push-back
;; (in reverse order)
(define (push-back lb i)
(letrec (
;; switch-buffers: c list * c list * int -> clist * clist
;; moves num-to-add characters from from to to.
;; (switch-buffers '(1 2 3 4) '(5 6 7 8) 2) =
;; (values '(3 4) '(2 1 5 6 7 8))
;; (switch-buffers '(4 3 2 1) '(5 6 7 8) 2) =
;; (values '(2 1) '(3 4 5 6 7 8))
(switch-buffers
(lambda (from to num-to-add)
(cond
((= 0 num-to-add) (values from to))
(else
(cond
((eq? #\newline (car from))
(set-lex-buffer-line!
lb
(sub1 (lex-buffer-line lb)))
(set-lex-buffer-offset!
lb
(car (lex-buffer-line-lengths lb)))
(set-lex-buffer-line-lengths!
lb
(cdr (lex-buffer-line-lengths lb))))
(else
(set-lex-buffer-col!
lb
(sub1 (lex-buffer-col lb)))))
(switch-buffers (cdr from)
(cons (car from) to)
(sub1 num-to-add)))))))
(let-values (((ret new-from)
(switch-buffers (lex-buffer-to lb)
(lex-buffer-from lb)
i)))
(set-lex-buffer-from! lb new-from)
(set-lex-buffer-to! lb null)
(set-lex-buffer-offset! lb (- (lex-buffer-offset lb) i))
(set-lex-buffer-line-lengths! lb null)
ret)))
(define-struct position (offset line col))
(define (get-position lb)
(make-position (lex-buffer-offset lb)
(lex-buffer-line lb)
(lex-buffer-col lb)))
)