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

218 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"
(lib "cffi.ss" "compiler"))
(provide lexer lexer-src-pos define-lex-abbrev define-lex-abbrevs
get-position position-offset position-line position-col position?
define-tokens define-empty-tokens)
(define-syntaxes (lexer-experiment lexer-src-pos-experiment)
(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 ((code (compile-table table))
(actions-stx `(vector ,@(vector->list (table-actions table))))
(wrap? wrap?))
(syntax
(compiled-lexer-body code actions-stx wrap?)))))))))))
(values
(build-lexer #f)
(build-lexer #t))))
(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-stx (table-start table))
(trans-table-stx (table-trans table))
(eof-table-stx (table-eof table))
(no-lookahead-stx (table-no-lookahead table))
(actions-stx `(vector ,@(vector->list (table-actions table))))
(wrap? wrap?))
(syntax
(lexer-body start-state-stx
trans-table-stx
eof-table-stx
actions-stx
no-lookahead-stx
wrap?)))))))))))
(values
(build-lexer #f)
(build-lexer #t))))
(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 (compiled-lexer-body lexer actions wrap?)
(lambda (ip)
(unless (input-port? ip)
(raise-type-error
'lexer
"input-port"
0
ip))
(let ((first-pos (get-position ip)))
(let-values (((longest-match-length longest-match-action)
(lexer ip peek-string)))
(do-match ip first-pos longest-match-length (vector-ref actions longest-match-action) wrap?)))))
(define (lexer-body start-state trans-table eof-table actions no-lookahead wrap?)
(lambda (ip)
(unless (input-port? ip)
(raise-type-error
'lexer
"input-port"
0
ip))
(let ((first-pos (get-position ip)))
(let lexer-loop (
;; current-state
(state start-state)
;; the character to transition on
(char (peek-string 1 0 ip))
;; 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 1))
(let ((next-state
(cond
((eof-object? char)
(vector-ref eof-table state))
(else
(vector-ref
trans-table
(+ (char->integer (string-ref char 0)) (* 256 state)))))))
(cond
((not next-state)
(do-match ip first-pos longest-match-length longest-match-action wrap?))
((vector-ref no-lookahead next-state)
(let ((act (vector-ref actions next-state)))
(do-match ip
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
(peek-string 1 length ip)
(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 (read-string longest-match-length lb))
(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))))
(cond
(wrap?
(let/ec ret
(list (longest-match-action
(lambda () first-pos)
(lambda () end-pos)
(lambda () match)
ret
lb)
first-pos
end-pos)))
(else
(longest-match-action
(lambda () first-pos)
(lambda () end-pos)
(lambda () match)
(lambda (x) x)
lb)))))
(define-struct position (offset line col))
(define (get-position ip)
(let-values (((line col off) (port-next-location ip)))
(make-position off line col)))
)