[ab]* 'a' couldn't derive 'aaa'

[curvedmark]

I don't really know how pegjs works, but I guess the reason might be that the three 'a's are matched first and when EOF is encountered, the last 'a' in the grammar is unmatched and thus causing the failure?

If trying alternatives is expensive and won't be implemented, is there any way to workaround it when such grammar is needed?

[michaelficarra]

Related: #57.

'a'? ('b'* 'a')+

[curvedmark]

The grammar actually means greedy matching in my case.

pegjs will have to try alternative matches in order to derive the input, much like how regexp works: when [ab]* has consumed the whole string and the rule doesn't match, it should reduce the consumption and try again, which might be expensive.

[michaelficarra]

@gravof: or you can rewrite it like I showed in my first comment.

[curvedmark]

Oh, thanks. went directly to the related issue, didn't pay much attention to the grammar you suggested.

It works. However, will nested repetition cause trouble? After seeing #26, I try to stay away from such pattern.

[curvedmark]

Probably related:

start
  = 'a'? 'a'

couldn't derive a

[prophile]

Greedy matching is how PEGs work. They are not regexes. :)

[dmajda]

Contrary to regular expressions, * and + modifiers in PEGs do not backtrack and just match greedily. This is how it is defined in the formalism. I do not plan to deviate from this behavior in PEG.js, nor do I think about introducing a special syntax for backtracking variants.

Closing this issue since the described behavior is not a bug.