Re: idiom for iterating

   From: Ville Laurikari <[email protected]>
   >
   > Ville: what do you think?

   This looks like a "negative lookahead assertion".  In Perl,
   /foo(?!bar)/ matches 'foo' if it's not followed by 'bar'.

   For a simple example case like this lookahead assertions seem easy
   enough to implement.  But it's not quite so simple to incorporate them
   into the non-backtracking matching algorithm used in TRE.

Hmmm... another justification to get PCRE as an optional
engine for CRM114.

   The simple cases can be implemented programmatically, outside the
   regex matching library, without adding any features in the regex
   matcher.  As for the more complex cases (ones where the lookahead
   expression is a full-blown regex and is just a part inside a complex
   regex), I'd argue that you should probably not be using a regex in the
   first place.

   I've considered lookahead and lookbehind assertions before, back when
   I was still actively developing TRE.

I think that Bryan Ford's stuff on PEGs (Parser Expression Grammars)
is right up that alley.... I was considering creating a useful PEG
but then I started doing exotic classifiers, and havent had...

       They are probably doable, but I
   probably ran out of paper or pencil or brain space or something, and
   gave up :)

I feel that way a lot, too.  Brain space is hard to budget.

Thanks!  And if you get bored... :)

	 - Bill Yerazunis


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