(guile.info.gz) Match Structures

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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? obj
      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'.
 
      (define s (string-match "[0-9][0-9][0-9][0-9]" "blah2002foo"))
      (match:substring s)
      => "2002"
 
      ;; match starting at offset 6 in the string
      (match:substring
        (string-match "[0-9][0-9][0-9][0-9]" "blah987654" 6))
      => "7654"
 
  -- Scheme Procedure: match:start match [n]
      Return the starting position of submatch number N.
 
    In the following example, the result is 4, since the match starts at
 character index 4:
 
      (define s (string-match "[0-9][0-9][0-9][0-9]" "blah2002foo"))
      (match:start s)
      => 4
 
  -- Scheme Procedure: match:end match [n]
      Return the ending position of submatch number N.
 
    In the following example, the result is 8, since the match runs
 between characters 4 and 8 (i.e. the "2002").
 
      (define s (string-match "[0-9][0-9][0-9][0-9]" "blah2002foo"))
      (match:end s)
      => 8
 
  -- Scheme Procedure: match:prefix match
      Return the unmatched portion of TARGET preceding the regexp match.
 
           (define s (string-match "[0-9][0-9][0-9][0-9]" "blah2002foo"))
           (match:prefix s)
           => "blah"
 
  -- Scheme Procedure: match:suffix match
      Return the unmatched portion of TARGET following the regexp match.
 
      (define s (string-match "[0-9][0-9][0-9][0-9]" "blah2002foo"))
      (match:suffix s)
      => "foo"
 
  -- 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.
 
      (define s (string-match "[0-9][0-9][0-9][0-9]" "blah2002foo"))
      (match:string s)
      => "blah2002foo"
 

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