On 8/8/11 6:11 PM, Francisco Mota wrote:
You are correct in assessing that .+ and .* expressions will probably never be useful. PEGs are completely different from regular expressions -- don't be misled by the syntactic similarities.
Fair enough.
To answer your first question, "Why should the repetition operators be greedy by default?" Because there is no backtracking*. So X* would always match the empty string, and X+ would always match X.
Ah. Without backtracking, that would be true. And as you point out:
In PEGs, there is a property of any parsing expression, and it is this: a parsing expression has only one possible match for any given string. This property enables packrat parsing. If you add backtracking*, you throw this property away.
Doh. So we lose the linear parse time guarantee. It still might be worth it, for string searching (as opposed to language parsing), but I see now that the result would not be PEG in important ways.
Thanks, - Joe _______________________________________________ PEG mailing list PEG@lists.csail.mit.edu https://lists.csail.mit.edu/mailman/listinfo/peg
