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

212 lines
7.6 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"
"private-lex/structs.ss")
(require (lib "readerr.ss" "syntax")
"private-lex/token.ss")
(provide lexer lexer-src-pos define-lex-abbrev define-lex-abbrevs
make-lex-buf
get-position position-offset position-line position-col position?
define-tokens define-empty-tokens)
(define-syntaxes (lexer lexer-src-pos)
(let ((build-lexer
(lambda (wrap)
(lambda (stx)
(syntax-case stx ()
((_)
(raise-syntax-error #f "empty lexer is not allowed" stx))
((_ re-act ...)
(begin
(for-each
(lambda (x)
(syntax-case x ()
((re act) (void))
(_ (raise-syntax-error 'lexer
"expects regular expression / action pairs"
x))))
(syntax->list (syntax (re-act ...))))
(let ((table (generate-table (syntax (re-act ...)) stx)))
(with-syntax ((start-state `,(table-start table))
(trans-table `,(table-trans table))
(eof-table `,(table-eof table))
(no-lookahead `,(table-no-lookahead table))
(actions `(vector ,@(vector->list (table-actions table)))))
(syntax (lambda (lb)
(lexer-body lb start-state trans-table eof-table actions no-lookahead wrap))))))))))))
(values
(build-lexer (lambda (x) x))
(build-lexer (lambda (x fp ep) (list x fp ep))))))
(define-syntax (define-lex-abbrev stx)
(syntax-case stx ()
((_ name re)
(syntax
(define-syntax name
(make-lex-abbrev (quote-syntax re)))))
(_
(raise-syntax-error
#f
"Form should be (define-lex-abbrev name re)"
stx))))
(define-syntax (define-lex-abbrevs stx)
(syntax-case stx ()
((_ x ...)
(let* ((abbrev (syntax->list (syntax (x ...))))
(r (map (lambda (a)
(syntax-case a ()
((name re)
(identifier? (syntax name))
(syntax (define-lex-abbrev name re)))
(_ (raise-syntax-error
'Lexer-abbreviation
"Form should be (identifier value)"
a))))
abbrev)))
(datum->syntax-object
#'here
(cons 'begin r)
stx)))
(_
(raise-syntax-error
#f
"Form should be (define-lex-abbrevs (name re) ...)"
stx))))
(define (lexer-body lb start-state trans-table eof-table actions no-lookahead wrap)
(unless (lex-buffer? lb)
(raise-type-error
'lexer
"lex-buf"
0
lb))
(let ((first-pos (get-position lb)))
(let lexer-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)
(do-match lb first-pos longest-match-length longest-match-action wrap))
((vector-ref no-lookahead next-state)
(let ((act (vector-ref actions next-state)))
(do-match lb
first-pos
(if act length longest-match-length)
(if act act longest-match-action)
wrap)))
(else
(let ((act (vector-ref actions next-state)))
(lexer-loop next-state
(next-char lb)
(if act
act
longest-match-action)
(add1 length)
(if act
length
longest-match-length)))))))))
(define (do-match lb first-pos longest-match-length longest-match-action wrap)
(let* ((match (get-match lb longest-match-length))
(end-pos (get-position lb)))
(if (not longest-match-action)
(raise-read-error
(format "lexer: No match found in input starting with: ~a" match)
#f
(position-line first-pos)
(position-col first-pos)
(position-offset first-pos)
(- (position-offset end-pos) (position-offset first-pos))))
(let/ec ret
(wrap
(longest-match-action
(lambda () first-pos)
(lambda () end-pos)
(lambda () match)
ret
lb)))))
;; Lex buffer is NOT thread safe
;; c = char | eof
;; lex-buf =
;; (make-lex-buffer input-port int int int int)
(define-struct lex-buffer (ip peek-amt line-start col-start offset-start))
;; make-lex-buf: input-port -> lex-buf
(define make-lex-buf
(case-lambda
((ip)
(cond
((not (input-port? ip))
(raise-type-error 'make-lex-buf "input-port" 0 ip))
(else
(make-lex-buffer ip 0 0 0 0))))
((ip offsets)
(cond
((not (input-port? ip))
(raise-type-error 'make-lex-buf "input-port" 0 ip offsets))
((or (not (= 3 (length offsets)))
(not (andmap integer? offsets))
(not (andmap exact? offsets))
(not (andmap (lambda (x) (>= x 0)) offsets)))
(raise-type-error 'make-lex-buf "list of 3 non-negative exact integers" 1 ip offsets))
(else
(make-lex-buffer ip 0 (car offsets) (cadr offsets) (caddr offsets)))))))
(define (next-char lb)
(let ((str (peek-string 1 (lex-buffer-peek-amt lb) (lex-buffer-ip lb))))
(cond
((string? str)
(set-lex-buffer-peek-amt! lb (add1 (lex-buffer-peek-amt lb)))
(string-ref str 0))
(else eof))))
;; get-match: lex-buf * int -> string
;; reads the next i characters.
(define (get-match lb i)
(set-lex-buffer-peek-amt! lb 0)
(read-string i (lex-buffer-ip lb)))
(define-struct position (offset line col))
(define (get-position lb)
(let-values (((line col off) (port-next-location (lex-buffer-ip lb))))
(if (and line col)
(make-position (+ (lex-buffer-offset-start lb) off)
(+ (lex-buffer-line-start lb) line)
(if (= line 1)
(+ (lex-buffer-col-start lb) col)
col))
(make-position (+ (lex-buffer-offset-start lb) off) #f #f))))
)