1. regex
    1. Introduction
    2. Usage
    3. Documentation
      1. grep
      2. glob->regexp
      3. regexp
      4. regexp?
      5. string-match
      6. string-match-positions
      7. string-search
      8. string-search-positions
      9. string-split-fields
      10. string-substitute
      11. string-substitute*
      12. regexp-escape
    4. Author
    5. License
    6. Version History

regex

Introduction

This extension provides the regular expression API that used to be available in CHICKEN releases before version 4.6.2. It is a thin wrapper around the functionality provided by irregex and is mostly intended to keep old code working.

Usage

(require-extension regex)

Documentation

grep

[procedure] (grep REGEX LIST [ACCESSOR])

Returns all items of LIST that match the regular expression REGEX. This procedure could be defined as follows:

(define (grep regex lst)
  (filter (lambda (x) (string-search regex x)) lst) )

ACCESSOR is an optional accessor-procedure applied to each element before doing the match. It should take a single argument and return a string that will then be used in the regular expression matching. ACCESSOR defaults to the identity function.

glob->regexp

[procedure] (glob->regexp PATTERN [SRE?])

Converts the file-pattern PATTERN into a regular expression.

(glob->regexp "foo.*")
=> "foo\..*"

PATTERN should follow "glob" syntax. Allowed wildcards are

*
[C...]
[C1-C2]
[-C...]
?

glob->regexp returns a regular expression object if the optional argument SRE? is false or not given, otherwise the SRE of the computed regular expression is returned.

regexp

[procedure] (regexp STRING [IGNORECASE [IGNORESPACE [UTF8]]])

Returns a precompiled regular expression object for string. The optional arguments IGNORECASE, IGNORESPACE and UTF8 specify whether the regular expression should be matched with case- or whitespace-differences ignored, or whether the string should be treated as containing UTF-8 encoded characters, respectively.

Note that code that uses regular expressions heavily should always use them in precompiled form, which is likely to be much faster than passing strings to any of the regular-expression routines described below.

regexp?

[procedure] (regexp? X)

Returns #t if X is a precompiled regular expression, or #f otherwise.

string-match

string-match-positions

[procedure] (string-match REGEXP STRING)
[procedure] (string-match-positions REGEXP STRING)

Matches the regular expression in REGEXP (a string or a precompiled regular expression) with STRING and returns either #f if the match failed, or a list of matching groups, where the first element is the complete match. For each matching group the result-list contains either: #f for a non-matching but optional group; a list of start- and end-position of the match in STRING (in the case of string-match-positions); or the matching substring (in the case of string-match). Note that the exact string is matched. For searching a pattern inside a string, see below. Note also that string-match is implemented by calling string-search with the regular expression wrapped in ^ ... $.

string-search-positions

[procedure] (string-search REGEXP STRING [START [RANGE]])
[procedure] (string-search-positions REGEXP STRING [START [RANGE]])

Searches for the first match of the regular expression in REGEXP with STRING. The search can be limited to RANGE characters.

string-split-fields

[procedure] (string-split-fields REGEXP STRING [MODE [START]])

Splits STRING into a list of fields according to MODE, where MODE can be the keyword #:infix (REGEXP matches field separator), the keyword #:suffix (REGEXP matches field terminator) or #t (REGEXP matches field), which is the default.

(define s "this is a string 1, 2, 3,")


(string-split-fields "\\w+" s)

  => ("this" "is" "a" "string" "1" "2" "3")


(string-split-fields "[^ ]+" s)

  => ("this" "is" "a" "string" "1," "2," "3,")

(string-split-fields " " s #:infix)

  => ("this" "is" "a" "string" "1," "2," "3,")

(string-split-fields "," s #:suffix)
 
  => ("this is a string 1" " 2" " 3")

string-substitute

[procedure] (string-substitute REGEXP SUBST STRING [MODE])

Searches substrings in STRING that match REGEXP and substitutes them with the string SUBST. The substitution can contain references to subexpressions in REGEXP with the \NUM notation, where NUM refers to the NUMth parenthesized expression. The optional argument MODE defaults to 1 and specifies the number of the match to be substituted. Any non-numeric index specifies that all matches are to be substituted.

(string-substitute "([0-9]+) (eggs|chicks)" "\\2 (\\1)" "99 eggs or 99 chicks" 2)
=> "99 eggs or chicks (99)"

Note that a regular expression that matches an empty string will signal an error.

string-substitute*

[procedure] (string-substitute* STRING SMAP [MODE])

Substitutes elements of STRING with string-substitute according to SMAP. SMAP should be an association-list where each element of the list is a pair of the form (MATCH . REPLACEMENT). Every occurrence of the regular expression MATCH in STRING will be replaced by the string REPLACEMENT

(string-substitute* "<h1>Hello, world!</h1>" '(("<[/A-Za-z0-9]+>" . "")))

=>  "Hello, world!"

regexp-escape

[procedure] (regexp-escape STRING)

Escapes all special characters in STRING with \, so that the string can be embedded into a regular expression.

(regexp-escape "^[0-9]+:.*$")
=>  "\\^\\[0-9\\]\\+:.\n.\\*\\$"

Author

felix winkelmann

License

Copyright (c) 2010, Felix L. Winkelmann All rights reserved.

Redistribution and use in source and binary forms, with or without modification, are permitted provided that the following conditions are met: 1. Redistributions of source code must retain the above copyright

  notice, this list of conditions and the following disclaimer.

2. 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.

3. The name of the authors may not be used to endorse or promote products

  derived from this software without specific prior written permission.

THIS SOFTWARE IS PROVIDED BY THE AUTHORS ``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 AUTHORS 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.

Version History

0.1
initial release