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96 lines
3.8 KiB
Markdown
96 lines
3.8 KiB
Markdown
Parsec
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======
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A monadic parser combinator library, written by Daan Leijen. Parsec is designed
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from scratch as an industrial-strength parser library. It is simple, safe, well
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documented, has extensive libraries, good error messages, and is fast.
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Some links:
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* [Parsec on Hackage](https://hackage.haskell.org/package/parsec),
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contains the generated documentation.
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* The 2001 paper written by Daan Leijen, some what outdated
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([PDF](https://web.archive.org/web/20140528151730/http://legacy.cs.uu.nl/daan/download/parsec/parsec.pdf),
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[HTML](https://web.archive.org/web/20140528151730/http://legacy.cs.uu.nl/daan/download/parsec/parsec.html),
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thanks to [archive.org](http://web.archive.org);
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and [PDF](https://research.microsoft.com/en-us/um/people/daan/download/parsec/parsec.pdf),
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thanks to Microsoft Research).
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* [Using Parsec](http://book.realworldhaskell.org/read/using-parsec.html),
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chapter 16 of [Real World Haskell](http://book.realworldhaskell.org/).
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* [An introduction to the Parsec library](http://kunigami.wordpress.com/2014/01/21/an-introduction-to-the-parsec-library)
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on Kunigami's blog.
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* [An introduction to parsing text in Haskell with Parsec](http://unbui.lt/#!/post/haskell-parsec-basics) on Wilson's blog.
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* Differences between Parsec and
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[Attoparsec](http://hackage.haskell.org/package/attoparsec)
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(Haskell's other prominent parser library) as explained in
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[an answer on StackExchange](http://stackoverflow.com/a/19213247).
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* Differences between Parsec and [Happy](http://www.haskell.org/happy)
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(Haskell's parser generator) as explained in two
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answers on separate StackExchange questions
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([1](http://stackoverflow.com/a/7270904),
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[2](http://stackoverflow.com/a/14775331)).
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By analyzing [Parsec's reverse dependencies on Hackage](http://packdeps.haskellers.com/reverse/parsec)
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we can find open source project that make use of Parsec. For example
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[bibtex](http://hackage.haskell.org/package/bibtex),
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[ConfigFile](http://hackage.haskell.org/package/ConfigFile),
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[csv](http://hackage.haskell.org/package/csv) and
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[hjson](http://hackage.haskell.org/package/hjson).
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## Getting started
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This requires a working version of `cabal` and `ghci`, which are part of
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any modern installation of Haskell, such as
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[Haskell Platform](https://www.haskell.org/platform).
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First install Parsec.
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cabal install parsec
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Below we show how a very simple parser that tests matching parentheses
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was made from GHCI (the interactive GHC environment), which we started
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with the `ghci` command).
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```
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Prelude> :m +Text.Parsec
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Prelude Text.Parsec> let parenSet = char '(' >> many parenSet >> char ')'
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Loading package transformers-0.3.0.0 ... linking ... done.
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Loading package array-0.5.0.0 ... linking ... done.
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Loading package deepseq-1.3.0.2 ... linking ... done.
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Loading package bytestring-0.10.4.0 ... linking ... done.
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Loading package mtl-2.1.3.1 ... linking ... done.
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Loading package text-1.1.1.3 ... linking ... done.
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Loading package parsec-3.1.5 ... linking ... done.
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Prelude Text.Parsec> let parens = (many parenSet >> eof) <|> eof
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Prelude Text.Parsec> parse parens "" "()"
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Right ()
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Prelude Text.Parsec> parse parens "" "()(())"
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Right ()
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Prelude Text.Parsec> parse parens "" "("
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Left (line 1, column 2):
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unexpected end of input
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expecting "(" or ")"
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```
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The `Right ()` results indicate successes: the parentheses matched.
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The `Left [...]` result indicates a parse failure, and is detailed
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with an error message.
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For a more thorough introduction to Parsec we recommend the links at
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the top of this README file.
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## Contributing
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Issues (bugs, feature requests or otherwise feedback) may be reported in
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[the Github issue tracker for this project](https://github.com/aslatter/parsec/issues).
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Pull-requests are also welcome.
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## License
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See the [LICENSE](https://github.com/aslatter/parsec/blob/master/LICENSE)
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file in the repository.
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