Choosing a Haskell parser

Question

There are many open sourced parser implementations available to us in Haskell. Parsec seems to be the standard for text parsing and attoparsec seems to be a popular choice for binary parsing but I don't know much beyond that. Is there a particular decision tree that you follow for choosing a parser implementation? Have you learned anything interesting about the strengths or weaknesses of the libraries?

Answer 1

You have several good options.

For lightweight parsing of String types:

• parsec
• polyparse

For packed bytestring parsing, e.g. of HTTP headers.

• attoparsec

For actual binary data most people use either:

• binary -- for lazy binary parsing
• cereal -- for strict binary parsing

The main question to ask yourself is what is the underlying string type?

• String?
• bytestring (strict)?
• bytestring (lazy)?
• unicode text

That decision largely determines which parser toolset you'll use.

The second question to ask is: do I already have a grammar for the data type? If so, I can just use happy

• The Happy parser generator

And obviously for custom data types there are a variety of good existing parsers:

• XML
  • haxml
  • xml-light
  • hxt
  • hexpat
• CSV
  • bytestring-csv
  • csv
• JSON
  • json
• rss/atom
  • feed

Answer 2

Just to add to Don's post: Personally, I quite like Text.ParserCombinators.ReadP (part of base) for no-nonsense quick and easy stuff. Particularly when Parsec seems like overkill.

There is a bytestringreadp library for the bytestring version, but it doesn't cover Char8 bytestrings, and I suspect attoparsec would be a better choice at this point.