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.
Dear Emily, version 0.1.1 [1] now contains a benchmark suite, where words of randomly generated languages are parsed with both parsers (ParsecT and StateT Text Maybe). For tiny to moderately sized languages, the speed- up is not huge but noticeable. (I need to work on improving test case generation.) I've been using this trick for a long time but only now decided to spin off a dedicated package. My experience with parsing large amounts of tabular data files shows there is a more substantial difference, although that might be due to my lack of understanding how to write optimized megaparsec parsers. Still your point is valid that this is merely anecdotal evidence. If time permits, I shall add a more realistic benchmark with randomly generated CSV data or Finn Bender's haskell-parsing-benchmarks [2]. Cheers, Olaf [1] https://hackage.haskell.org/package/faster-megaparsec-0.1.1.0 [2] https://gitlab.com/FinnBender/haskell-parsing-benchmarks
On Tue, Nov 08, 2022 at 1:31 PM, Olaf Klinke < olf at aatal- apotheke.de > wrote:
Dear Haskellers,
megaparsec [1] is a parsing library with excellent error reporting.
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
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
Being parser to 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