Do you provide reproducible benchmarks for these claims? I'd love to see the outcome for various types of projects to make the choice for myself. Unsubstantiated claims of "This is Faster™️" are the path to shame and treachery. On Tue, Nov 08, 2022 at 1:31 PM, Olaf Klinke < olf@aatal-apotheke.de > wrote:
Dear Haskellers,
megaparsec [1] is a parsing library with excellent error reporting. Being able to emit decent parse error messages is traded off against speed, however. Wouldn't it be nice to have a faster parser for your daily parsing needs, but obtain megaparsec's informative error messages for the rare cases when things go wrong?
Thanks to megaparsec's parser type class, MonadParsec, you can have both: I wrote a MonadParsec instance for StateT s Maybe (s being the input stream type such as Text or ByteString) which does not do all the bookkeeping ParsecT needs to do. If you manage to write your parser only using the type class primitives, then you can specialize your parser to StateT s Maybe. Only if that returns Nothing specialize again to ParsecT Void s and parse the input again, thus obtaining a decent error message. The package faster-megaparsec [1,2] provides a convenient function to do just that.
Of course StateT s Maybe can not provide all the features ParsecT has: * StateT s Maybe is always backtracking. * It does not know the offset in the stream. * It must hold the entire input stream in memory for a second pass, so no garbage collecting the consumed input while parsing. So if your parsing relies on non-backtracking choice, stream offset or garbage-collecting input while parsing, you can not use faster- megaparsec as a drop-in replacement.
Happy parsing! Olaf
[1] https:/ / hackage. haskell. org/ package/ megaparsec ( https://hackage.haskell.org/package/megaparsec ) [2] https:/ / hackage. haskell. org/ package/ faster-megaparsec ( https://hackage.haskell.org/package/faster-megaparsec ) [3] https://hub.darcs.net/olf/faster-megaparsec
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