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lexgen is a lexer generator comprised in its core of only four small procedures. The programmer combines these procedures into regular expression pattern matchers.
A pattern matcher procedure takes a list of streams, and returns a new list of streams advanced by every combination allowed by the pattern matcher function. A stream is defined as a list that contains a list of characters consumed by the pattern matcher, and a list of characters not yet consumed.
Note that the number of streams returned by a pattern matcher typically won't match the number of streams passed in. If the pattern doesn't match at all, the empty list is returned.
Every combinator procedure in this library returns a procedure that takes in a continuation procedure and a list of streams as arguments.
Basic procedures[procedure] (tok TOKEN PROC) => MATCHER
Procedure tok builds a pattern matcher function that, for each stream given, applies a procedure to the given token TOKEN and an input character. If the procedure returns a true value, that value is prepended to the list of consumed elements, and the input character is removed from the list of input elements.[procedure] (seq MATCHER1 MATCHER2) => MATCHER
seq builds a matcher that matches a sequence of patterns.[procedure] (bar MATCHER1 MATCHER2) => MATCHER
bar matches either of two patterns. It's analogous to patterns separated by | in traditional regular expressions.[procedure] (star MATCHER) => MATCHER
star is an implementation of the Kleene closure. It is analogous to * in traditional regular expressions.
These procedures are built from the previous four and are provided for convenience.[procedure] (try PROC) => PROC
Converts a binary predicate procedure to a binary procedure that returns its right argument when the predicate is true, and false otherwise.[procedure] (char CHAR) => MATCHER
Matches a single character.[procedure] (lst MATCHER-LIST) => MATCHER
Constructs a matcher for the sequence of matchers in MATCHER-LIST.[procedure] (pos MATCHER) => MATCHER
Positive closure. Analogous to +.[procedure] (opt MATCHER) => MATCHER
Optional pattern. Analogous to ?.[procedure] (set CHAR-SET) => MATCHER
Matches any of a SRFI-14 set of characters.[procedure] (range CHAR CHAR) => MATCHER
Matches a range of characters. Analogous to character class .[procedure] (lit STRING) => MATCHER
Matches a literal string s.
<procedure>(bind F P) => MATCHER
Given a rule P and function F, returns a matcher that first applies P to the input stream, then applies F to the returned list of consumed tokens, and returns the result and the remainder of the input stream.
<procedure>(rebind F G P) => MATCHER
Given a rule P and procedures F and G, returns a matcher that first applies F to the input stream, then applies P to the resulting stream, then applies G to the resulting list of consumed elements and returns the result along with the remainder of the input stream.
<procedure>(drop P) => MATCHER
Given a rule P, returns a matcher that always returns an empty list of consumed tokens when P succeeds.
Lexer procedures[procedure] (longest STREAM-LIST) => STREAM
Takes the resulting streams produced by the application of a pattern on a stream (or streams) and selects the longest match if one exists. If STREAM-LIST is empty, it returns #F.[procedure] (lex MATCHER ERROR STRING) => CHAR-LIST
lex takes a pattern and a string, turns the string into a list of streams (containing one stream), applies the pattern, and returns the longest match. Argument ERROR is a single-argument procedure called when the pattern does not match anything.
A stream is a list that can take one of two forms:
1) A list of two elements: the first element is a list of elements consumed by the pattern matcher; the second element is a list of elements not yet consumed. E.g., the list
((#\a) (#\b #\c #\d #\e))
represents a stream that contains the consumed character a, and the unconsumed characters b c d e.
2) A list of three elements: the first two elements are as before, but the third element is a procedure that is applied to the tail of the unconsumed list, in order to obtain the next character. E.g., the list:
((#\a) (#\b <port>) <procedure (lambda (in) (list (read-char in) in))>
represents a stream that contains the consumed character a, the unconsumed character b, and an input port to read subsequent characters from; and a procedure that reads one character from the input port, and returns it along with the modified port. Note that the use of side-effecting structures such as ports will lead to erroneous results with backtracking parsers.[procedure] (stream-unfold INIT F G)
A helper procedure to transform streams from one format to another. Procedure F must be a procedure of two arguments, a state and a list of unconsumed characters. Procedure G is applied to an unconsumed element, and is expected to return the original element representation, before F was applied to the unconsumed stream.
(use srfi-1 lexgen) ;; A pattern to match floating point numbers. ;; "-"?(([0-9]+(\\.[0-9]+)?)|(\\.[0-9]+))([eE][+-]?[0-9]+)? (define numpat (let* ((digit (range #\0 #\9)) (digits (pos digit)) (fraction (seq (char #\.) digits)) (significand (bar (seq digits (opt fraction)) fraction)) (exp (seq (set "eE") (seq (opt (set "+-")) digits))) (sign (opt (char #\-)))) (seq sign (seq significand (opt exp))))) (define (err s) (print "lexical error on stream: " s) (list)) (lex numpat err "-123.45e-6") ;; Tokens with position information (define-record-type postok (make-postok pos token) postok? (pos postok-pos ) (token postok-token ) ) (define-record-printer (postok x out) (fprintf out "#<token ~A: ~A>" (postok-pos x) (postok-token x))) (define pos? pair?) (define pos-row car) (define pos-col cdr) (define make-pos cons) ;; Converts an input stream to a stream with position information: (define (stream-pos begtok) (and (postok? begtok) (stream-unfold begtok (lambda (begtok strm) (if (null? strm) '() (let* ((pos0 (postok-pos begtok)) (pos1 (let ((row0 (pos-row pos0)) (col0 (pos-col pos0))) (case (car strm) ((#\newline) (make-pos (+ 1 row0) 1)) ((#\return) (make-pos row0 1)) (else (make-pos row0 (+ 1 col0)))))) (res (cons (make-postok pos1 (car strm)) (cdr strm)))) res))) postok-token))) (define begpos (make-pos 1 0)) (define (getpos p) (let ((f (lambda (in) (and (pair? in) (pair? (cdr in)) (postok-pos (cadr in))))) (g (lambda (i s) (list (make-postok i (car s)))))) (rebind f g p))) (define pos-numpat-stream (list ((stream-pos (make-postok begpos 'start)) `(() ,(string->list "-123.45e-6"))))) (define pbnumpat (let* ((digit (range #\0 #\9)) (digits (star digit)) (fraction (seq (char #\.) digits)) (significand (bar (seq digits (opt fraction)) fraction)) (exp (seq (set "eE") (seq (opt (set "+-")) digits))) (sign (opt (char #\-)) ) (pat (seq (getpos (bind make-sign sign)) (seq (getpos (bind make-significand (longest significand))) (getpos (bind make-exp (longest (opt exp)))))))) pat)) (define (pos-num-parser s) (car (lex pbnumpat err s)))
- 3.1 Added rebind combinator and stream-unfold procedure
- 3.0 Added an extension mechanism for input streams of different types (to be elaborated and documented in subsequent versions).
- 2.6 Added bind and drop combinators
- 2.5 The seq combinator checks whether the first parser in the sequence has failed
- 2.4 Added (require-library srfi-1); using lset<= instead of equal? in star
- 2.3 Bug fix in procedure range; added procedure cps-table
- 2.2 Bug fix in procedure star
- 2.1 Added procedure lst
- 2.0 Core procedures rewritten in continuation-passing style
- 1.5 Using (require-extension srfi-1)
- 1.4 Ported to Chicken 4
- 1.2 Added procedures try and tok (supersedes pred)
- 1.0 Initial release
Based on the SML lexer generator by Thant Tessman.
Copyright 2009 Ivan Raikov. All rights reserved. Redistribution and use in source and binary forms, with or without modification, are permitted provided that the following conditions are met: Redistributions of source code must retain the above copyright notice, this list of conditions and the following disclaimer. Redistributions in binary form must reproduce the above copyright notice, this list of conditions and the following disclaimer in the documentation and/or other materials provided with the distribution. Neither the name of the author nor the names of its contributors may be used to endorse or promote products derived from this software without specific prior written permission. THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDERS OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.