TIP #113 Version 1.5: Multi-Line Searches in the Text Widget

This is not necessarily the current version of this TIP.

Abstract

This TIP proposes enhancing the implementation of the $textwidget search subcommand to allow matching of both exact strings and regexp patterns which span multiple lines, and to allow reporting on all matches.

Proposal

If the string/pattern given to the search subcommand contains sub-strings/patterns which match newlines, then it will be possible for that command to return a match which spans multiple lines. Where a match could occur both within a single line and across multiple lines, the first such match will be found, and the length of the match will follow the usual regexp rules, as documented in the regexp man page.

This can be implemented very efficiently, given the TCL_REG_CANMATCH flag supported by the regexp library, with no impact at all on the speed of matching single lines.

In addition, if a new -all option is given to the search subcommand, then all matches within the given range will be reported. This means the return result of the command will be a list of indices, and, if a -count var option was given, var will be set to a list of match-index-lengths.

The text widget man page will need updating to reflect the new ''-all' option, and to remove the "single line" caveat.

Reference implementation

This is available from:

http://sourceforge.net/tracker/?func=detail&aid=621901&group_id=12997&atid=312997

(However, this patch has to workaround a bug in Tcl's unicode string manipulation, so search performance is probably impacted)

Issues

Regexp searches in text widgets always operate as if the -lineanchor flag has been given. This is needed for backwards compatibility (so ^$ match at the beginning and end of each line respectively). The current implementation also forces the -linestop flag, although it is potentially useful to allow user-control over that (so .* can match across multiple lines).

On the implementation side, it might be interesting to abstract the search interface away from the text widget, so that it could in principle be applied to any line-based textual source.

As in the single-line matching implementation in Tcl 8.x, the lack of support for backwards matching in Tcl's regexp library means that backwards matching can only be implemented as repeated forward matches, with a commensurate performance penalty (the solution to which is outside the scope of this tip).

Copyright

This document has been placed in the public domain.

This is not necessarily the current version of this TIP.