Parsec

A monadic parser combinator library, written by Daan Leijen. Parsec is designed from scratch as an industrial-strength parser library. It is simple, safe, well documented, has extensive libraries, good error messages, and is fast.

Some links:

• Parsec on Hackage, contains the generated documentation.
• The 2001 paper written by Daan Leijen, some what outdated (PDF, HTML, thanks to archive.org; and PDF, thanks to Microsoft Research).
• Using Parsec, chapter 16 of Real World Haskell.
• An introduction to the Parsec library on Kunigami’s blog.
• An introduction to parsing text in Haskell with Parsec on Wilson’s blog.
• Differences between Parsec and Attoparsec (Haskell’s other prominent parser library) as explained in an answer on StackExchange.
• Differences between Parsec and Happy (Haskell’s parser generator) as explained in two answers on separate StackExchange questions (1, 2).

By analyzing Parsec’s reverse dependencies on Hackage we can find open source project that make use of Parsec. For example bibtex, ConfigFile, csv and hjson.

Getting started

This requires a working version of cabal and ghci, which are part of any modern installation of Haskell, such as Haskell Platform.

First install Parsec.

cabal install parsec

Below we show how a very simple parser that tests matching parentheses was made from GHCI (the interactive GHC environment), which we started with the ghci command).

Prelude> :m +Text.Parsec
Prelude Text.Parsec> let parenSet = char '(' >> many parenSet >> char ')'
Loading package transformers-0.3.0.0 ... linking ... done.
Loading package array-0.5.0.0 ... linking ... done.
Loading package deepseq-1.3.0.2 ... linking ... done.
Loading package bytestring-0.10.4.0 ... linking ... done.
Loading package mtl-2.1.3.1 ... linking ... done.
Loading package text-1.1.1.3 ... linking ... done.
Loading package parsec-3.1.5 ... linking ... done.
Prelude Text.Parsec> let parens = (many parenSet >> eof) <|> eof
Prelude Text.Parsec> parse parens "" "()"
Right ()
Prelude Text.Parsec> parse parens "" "()(())"
Right ()
Prelude Text.Parsec> parse parens "" "("
Left (line 1, column 2):
unexpected end of input
expecting "(" or ")"

The Right () results indicate successes: the parentheses matched. The Left [...] result indicates a parse failure, and is detailed with an error message.

For a more thorough introduction to Parsec we recommend the links at the top of this README file.

Contributing

Issues (bugs, feature requests or otherwise feedback) may be reported in the Github issue tracker for this project.

Pull-requests are also welcome.

License

See the LICENSE file in the repository.