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21.5.2 Match Structures

A match structure is the object returned by string-match and regexp-exec. It describes which portion of a string, if any, matched the given regular expression. Match structures include: a reference to the string that was checked for matches; the starting and ending positions of the regexp match; and, if the regexp included any parenthesized subexpressions, the starting and ending positions of each submatch.

In each of the regexp match functions described below, the match argument must be a match structure returned by a previous call to string-match or regexp-exec. Most of these functions return some information about the original target string that was matched against a regular expression; we will call that string target for easy reference.

— Scheme Procedure: regexp-match? match

Return #t if obj is a match structure returned by a previous call to regexp-exec, or #f otherwise.

— Scheme Procedure: match:substring match [n]

Return the portion of target matched by subexpression number n. Submatch 0 (the default) represents the entire regexp match. If the regular expression as a whole matched, but the subexpression number n did not match, return #f.

— Scheme Procedure: match:start match [n]

Return the starting position of submatch number n.

— Scheme Procedure: match:end match [n]

Return the ending position of submatch number n.

— Scheme Procedure: match:prefix match

Return the unmatched portion of target preceding the regexp match.

— Scheme Procedure: match:suffix match

Return the unmatched portion of target following the regexp match.

— Scheme Procedure: match:count match

Return the number of parenthesized subexpressions from match. Note that the entire regular expression match itself counts as a subexpression, and failed submatches are included in the count.

— Scheme Procedure: match:string match

Return the original target string.