* Omari Norman
The Parsec documentation says that Parsec performs best on predictive grammars, and Parsec does not backtrack by default to improve performance (though this also improves error messages).
On the other hand, I notice that attoparsec and polyparse backtrack by default, and attoparsec claims to be faster than Parsec (I can't remember if polyparse makes this claim).
Attoparsec's goal is to be fast in practice. It achieves this goal by making some compromises -- e.g. being potentially asymptotically slower and admitting potential memory leaks, because of the unrestricted backtracking. Often this doesn't happen or isn't significant, but I believe users should be aware of this. I think the speed benefit of not restricting backtracking comes just from allocating less continuations. Bryan, can you confirm? Although Polyparse permits backtracking by default, it is still closer to Parsec in that it allows controlled backtracking. -- Roman I. Cheplyaka :: http://ro-che.info/