[Haskell-cafe] [ANN] faster-megaparsec

[Emily Pillmore]

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 at 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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