chickadee » irregex » irregex-fold

This performs a fold operation over every non-overlapping place <irx> occurs in the string str.

The <kons> procedure takes the following signature:

(<kons> <from-index> <match> <seed>)

where <from-index> is the index from where we started searching (initially <start> and thereafter the end index of the last match), <match> is the resulting match-data object, and <seed> is the accumulated fold result starting with <knil>.

The rationale for providing the <from-index> (which is not provided in the SCSH regexp-fold utility), is because this information is useful (e.g. for extracting the unmatched portion of the string before the current match, as needed in irregex-replace), and not otherwise directly accessible.

The optional <finish> takes two arguments:

(<finish> <from-index> <seed>)

which simiarly allows you to pick up the unmatched tail of the string, and defaults to just returning the <seed>.

<start> and <end> are numeric indices letting you specify the boundaries of the string on which you want to fold.

To extract all instances of a match out of a string, you can use

(map irregex-match-substring
     (irregex-fold <irx>
                   (lambda (i m s) (cons m s))
		   '()
		   <str>
		   (lambda (i s) (reverse s))))