StringCheckForChar - Cookbook - s c h e m a t i c s : c o o k b o o k

Checking a String for a Character

Problem

You need to find out if a string contains a character. You probably want to know the index of where the character was found.

This isn't built into R5RS, but is built into SRFI-13, in the form of string-index and string-index-right. string-index can look for a character, a char-set (see SRFI-14), or can be controlled by a predicate. So if you want to find the comma in the string "Hello, World!", the following 3 forms are equivalent:

(require (lib "string.ss" "srfi" "13")
           (lib "char-set.ss" "srfi" "14"))
> (string-index "Hello, World!" #\,)
5
> (string-index "Hello, World!" (char-set #\,))
5
> (string-index "Hello, World!" (lambda (c) (eq? c #\,)))
5

string-index returns #f if no match is found:

> (string-index "Hello, World!" #\?)
#f

Discussion

SRFI-14's char-set is pretty cool in its own right. Let's say you want to find all the punctuation in the same string; the following returns a list of the indices where any puctuation is found:

> (let loop ((next-index (string-index "Hello, World!" char-set:punctuation 0))
           (result '()))
  (if (not next-index)
      result
      (loop (string-index "Hello, World!" 
                          char-set:punctuation 
                          (+ 1 next-index)) 
            (cons next-index result))))
(12 5)

-- GordonWeakliem - 09 Apr 2004

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TopicType:	Recipe
ParentTopic:	StringRecipes
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Current Rev: r1.3 - 18 May 2004 - 22:50 GMT - BrentAFulgham, Revision History:Diffs | r1.4 | > | r1.3 | > | r1.2

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s c h e m a t i c s : c o o k b o o k

Checking a String for a Character

Problem

Solution

Discussion