paren:backward-match

• (paren:backward-match text start end parens quotes comments containing? cache) -> (union integer #f)
      text : (instance text%)
      start : exact-integer
      end : exact-integer
      parens : (listof (cons string string))
      quotes : (listof (cons string string))
      comments : (listof string)
      containing? = #f : boolean
      cache = #f : (union #f (instance match-cache:%))

  Returns the position in text that ``opens'' the text ending at start, or #f if no opening position is found (either because a parenthesis mis-match is discovered or the end boundary was reached). The match must occur before end (inclusive). Note that start > end, since start specifies the starting position of the search, not the earliest buffer position to be considered.

  Spaces immediately preceding start are skipped. If the text at start is a close parenthesis or close quote, then the matching position is the opening parenthesis or quote. If a comment immediately precedes start, then the comment is skipped as whitespace. If an opening parenthesis immediately precedes start, then the matching position is start - 1. Otherwise, the matching position is the first whitespace or parenthesis character before start.

  If containing? is not #f, then the matching procedure is modified as follows:

  • Searching iterates backwards until some search fails. Then, the location of the last successful search is returned.
  • If a mis-match is detected, then #f is returned.
  • If there are no matches (and no mis-matches) before start, start itself is returned.

  If cache is not #f, it must be an instance of match-cache:%. A cache object can be used to speed up successive calls to paren:backward-match. However, a buffer using a cache must call the cache's invalidate method when the buffer is modified. Different caches should be used for forward and backward matching. See the match cache section for more information.