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92 lines
3.9 KiB
Markdown
92 lines
3.9 KiB
Markdown
# Megaparsec
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[](http://opensource.org/licenses/BSD-3-Clause)
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[](https://hackage.haskell.org/package/megaparsec)
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[](https://travis-ci.org/mrkkrp/megaparsec)
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[](https://coveralls.io/github/mrkkrp/megaparsec?branch=master)
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This is industrial-strength monadic parser combinator library. Megaparsec is
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a fork of Parsec library originally written by Daan Leijen.
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Megaparsec is different from Parsec in the following ways:
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* Better error messages. We test our error messages using dense QuickCheck
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tests. Good error messages are just as important for us as correct return
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values of our parsers. Megaparsec will be especially useful if you write
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compiler or interpreter for some language.
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* Some quirks and “buggy features” (as well as plain bugs) of original
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Parsec are fixed. There is no undocumented surprising stuff in Megaparsec.
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* Better support for Unicode parsing in `Text.Megaparsec.Char`.
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* Megaparsec has more powerful combinators and can parse languages where
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indentation matters.
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* Comprehensive QuickCheck test suite covering nearly 100% of our code.
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* We have benchmarks to detect performance regressions.
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* Better documentation, with 100% of functions covered, without typos and
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obsolete information, with working examples. Megaparsec's documentation is
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well-structured and doesn't contain things useless to end user.
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* Megaparsec's code is clearer and doesn't contain “magic” found in original
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Parsec.
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* Megaparsec looks into the future, it does not contain code that serves for
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compatibility purposes, it also requires more recent version of `base`.
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## Megaparsec vs Parsec
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There are good reasons to use Parsec:
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* You need to work with legacy code or with older versions of GHC (≤ 7.10).
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And that's it. In other cases you should prefer Megaparsec for your own
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sake. If you think you have a reason to use Parsec other than listed here,
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open an issue. We are glad to hear from you.
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## Megaparsec vs Parsers
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There is [parsers](https://hackage.haskell.org/package/parsers) package,
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which is great. You can use it, but consider the following:
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* It depends on *both* Attoparsec and Parsec, which means you always grab
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useless code installing it. This is ridiculous, by the way, because this
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package is supposed to be useful for parser builders, so they can write
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basic core functionality and get the rest “for free”. But with these
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useful functions you get two more parsers as dependencies.
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* It currently has a bug in definition of `lookAhead` for various monad
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transformers like `StateT`, etc. which is visible when you create
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backtracking state via monad stack, not via built-in features. See #27.
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We intended to use Parsers library in Megaparsec at some point, but aside
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from already mentioned flaws the library has different conventions for
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naming of things, different set of “core” functions, etc., different
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approach to lexer. So it didn't happen, Megaparsec has minimal dependencies,
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it is feature-rich and self-contained.
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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/mrkkrp/megaparsec/issues).
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Pull-requests are also welcome (and yes, they will get attention and will be
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merged quickly if they are good, we are progressive folks).
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## Spread the Word
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Many people still don't know about Megaparsec, you can help the project by
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writing about it in a blog, creating a tutorial or something like that. This
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is highly appreciated.
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## License
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Copyright © 2015 Megaparsec contributors<br>
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Copyright © 2007 Paolo Martini<br>
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Copyright © 1999–2000 Daan Leijen
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Distributed under BSD3 license.
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