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