Ho about this (replacement for yours, or just replace in PPChoiceParser - but it will result in different behavior for that method outside of your particular parser, so beware):

parseOn: aStream
"This is optimized code that avoids unnecessary block activations, do not change. When all choices fail, the last failure is answered."

| element longest |
longest := #( 0 nil ).
1 to: parsers size do: [ :index |
element := (parsers at: index)
parseOn: aStream.
element isPetitFailure
ifTrue: [ aStream position > longest first ifTrue: [ longest at: 1 put: aStream position; at: 2 put: element ] ]
ifFalse: [ ^ element ] ].
aStream position: longest first.
^ element

I had a need for it in the past (and, just now, in fact - so minimally tested just now).

-cbc


On Wed, Nov 20, 2013 at 2:15 AM, Norbert Hartl <norbert@hartl.name> wrote:
I talked to Lukas two years ago about parsing the longest match [1]. He committed it to PetitBeta back then. Now I need it and I had a look at the current parsers but didn�t find one that can do the same. Is there a parser that can do longest match?

If not I would propose adding that to the default petit parser package. Lukas� proposal back then was

LongestChoiceParser>>parseOn: aStream
	| start element longestEnd longestElement |
	start := aStream position.
	1 to: parsers size do: [ :index |
		element := (parsers at: index)
			parseOn: aStream.
		(longestEnd isNil or: [ longestEnd < aStream position ]) ifTrue: [
			longestEnd := aStream position.
			longestElement := element ].
		aStream position: start ].
	aStream position: longestEnd.
	^ longestElement

Norbert

[1]�http://www.iam.unibe.ch/pipermail/moose-dev/2011-July/009365.html