# Difference between revisions of "Example code"

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− | == Example Code == |
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+ | To get a feel for what real world Haskell looks like, here are some |
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+ | examples from various popular [[Libraries_and_tools|Haskell projects]]. |
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+ | To start learning the language, good places to start are |
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+ | [[Learning Haskell]], |
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+ | [[Haskell in 5 steps]], and |
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+ | [[Books and tutorials]]. |
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− | This is a collection of example code. It is intended to take the role of the old Wiki area [http://haskell.org/hawiki/CodeOnTheWiki CodeOnTheWiki]. Contributors of code to the old area are encouraged to bring their code over here. This should only be done by the original author because anything on these pages is automatically licensed under the Simple Permissive License ([[HaskellWiki:Copyrights]]). |
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+ | More code may be found [http://www.haskell.org/haskellwiki/Category:Code on the wiki]. |
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− | [[Prelude extensions]]: Simple things you've always wished were in the Prelude. |
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+ | <!-- |
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+ | Some lines are commented out for later update |
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+ | --> |
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− | [[Gallery]]: Complete small programs. |
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+ | === Library code === |
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− | [[Blow_your_mind|Blow your mind]]: Short, useful, cool, magical examples, which should incite the reader's curiosity and (hopefully) lead him to a deeper understanding of advanced Haskell concepts. |
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+ | Library code usually differs from application code: it is often highly |
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+ | structured, and documented with [http://www.haskell.org/haddock/ haddock], |
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+ | and can be rather optimised. Some instructive examples (syntax |
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+ | highlighting by [http://www.cs.york.ac.uk/fp/darcs/hscolour/ hscolour]): |
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− | [[Sudoku]]: Solvers for popular puzzle [http://en.wikipedia.org/wiki/Sudoku Sudoku]. |
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+ | * [http://www.haskell.org/ghc/docs/latest/html/libraries/base/src/Prelude.html A Haskell Prelude.hs], foundational Haskell library ([http://www.haskell.org/ghc/docs/latest/html/libraries/base/Prelude.html docs]) |
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− | [[NewMonads]]: Useful monads that are not in the main library. |
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+ | * [[Simple_Unix_tools | Unix.hs]], simple unix tools, for beginner Haskellers |
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+ | |||

+ | * [http://hackage.haskell.org/packages/archive/base/latest/doc/html/src/Data.List.html Data.List], the standard list library ([http://hackage.haskell.org/packages/archive/base/latest/doc/html/Data-List.html docs]) |
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+ | |||

+ | * [http://hackage.haskell.org/packages/archive/base/latest/doc/html/src/Data.Maybe.html Data.Maybe], the <code>Maybe</code> type ([http://hackage.haskell.org/packages/archive/base/latest/doc/html/Data-Maybe.html docs]) |
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+ | |||

+ | * [http://hackage.haskell.org/packages/archive/containers/latest/doc/html/src/Data.Map.html Data.Map], the standard finite map ([http://www.haskell.org/ghc/docs/latest/html/libraries/containers-0.4.2.1/index.html docs]) |
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+ | |||

+ | * [http://hackage.haskell.org/packages/archive/containers/latest/doc/html/src/Data.Graph.html Data.Graph], a graph type ([http://hackage.haskell.org/packages/archive/containers/latest/doc/html/Data-Graph.html docs]) |
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+ | |||

+ | * [http://hackage.haskell.org/packages/archive/base/latest/doc/html/src/Control.Monad.html Control.Monad], basic monad support ([http://hackage.haskell.org/packages/archive/base/latest/doc/html/Control-Monad.html docs]) |
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+ | |||

+ | * [https://github.com/nick8325/quickcheck QuickCheck], a testing framework ([http://hackage.haskell.org/package/QuickCheck docs]) |
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+ | |||

+ | * [http://hackage.haskell.org/packages/archive/pretty/latest/doc/html/src/Text-PrettyPrint-HughesPJ.html PrettyPrint.hs], a pretty printing library ([http://hackage.haskell.org/package/pretty docs]) |
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+ | |||

+ | * [http://hackage.haskell.org/packages/archive/transformers/latest/doc/html/src/Control-Monad-Trans-State-Lazy.html Control.Monad.Trans.State.Lazy], a state monad ([http://hackage.haskell.org/packages/archive/transformers/latest/doc/html/Control-Monad-Trans-State-Lazy.html docs]) |
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+ | <!-- |
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+ | * [http://www.cse.unsw.edu.au/~dons/data/Music.html Music.hs], a music composition system (literate latex-style Haskell) ([http://darcs.haskell.org/haskore/src/Haskore/Music.lhs raw], [http://www.haskell.org/haskore/ home]) |
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+ | --> |
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+ | |||

+ | * [http://www.ninebynine.org/Software/Swish-0.2.1/HaskellRDF/Dfa/Dfa.lhs Dfa.lhs], finite automata (literate Bird-style Haskell) |
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+ | |||

+ | * [http://www.polyomino.f2s.com/david/haskell/hs/RedBlackTree.hs.txt RedBlackTree.hs], a red-black tree |
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+ | <!-- |
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+ | * [http://www.cse.unsw.edu.au/~dons/data/Prime.html Prime.hs], prime numbers ([http://andrew.bromage.org/darcs/numbertheory/Math/Prime.hs raw]) |
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+ | --> |
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+ | |||

+ | * [http://hackage.haskell.org/packages/archive/base/latest/doc/html/src/Data.Foldable.html Data.Foldable], traversable data structures ([http://hackage.haskell.org/packages/archive/base/latest/doc/html/Data-Foldable.html docs]) |
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+ | |||

+ | * [https://github.com/haskell/bytestring Data.ByteString], high-performance string type ([http://code.haskell.org/bytestring/Data/ByteString.hs raw], [http://hackage.haskell.org/package/bytestring docs]) |
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+ | |||

+ | * [https://github.com/feuerbach/smallcheck SmallCheck], a testing framework ([https://raw.github.com/feuerbach/smallcheck/master/Test/SmallCheck.hs raw], [http://hackage.haskell.org/package/smallcheck docs]) |
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+ | |||

+ | * [http://www.haskell.org/haskellwiki/Darcs_repositories More code ...] |
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+ | |||

+ | === Application code === |
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+ | |||

+ | Code from popular Haskell applications. Such code often makes use of a |
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+ | monadic IO, and sometimes other advanced features such as concurrency: |
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+ | |||

+ | <!-- |
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+ | * [http://nanardon.zarb.org/darcs/darcs/PatchCommute.lhs Darcs], a revision control system (uses literate latex Haskell style) ([http://darcs.net home]) |
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+ | --> |
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+ | * [http://svn.openfoundry.org/pugs/src/Pugs/Eval.hs Pugs], a perl6 implementation ([http://pugscode.org home]) |
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+ | |||

+ | * [https://github.com/yi-editor/yi/blob/master/yi-core/src/Yi/Core.hs Yi], a text editor, ([http://www.haskell.org/haskellwiki/Yi home], [https://raw.githubusercontent.com/yi-editor/yi/master/yi-core/src/Yi/Core.hs raw], [http://hackage.haskell.org/package/yi doc]) |
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+ | <!-- |
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+ | * [http://darcs.haskell.org/~lemmih/downNova/src/Torrent.hs DownNova], a file downloading program |
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+ | --> |
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+ | |||

+ | * [http://www.cs.york.ac.uk/fp/darcs/cpphs/Language/Preprocessor/Cpphs/Tokenise.hs cpphs], an implementation of the C preprocessor ([https://archives.haskell.org/projects.haskell.org/cpphs/ home]) |
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+ | |||

+ | * [http://darcs.haskell.org/ghc/compiler/simplCore/Simplify.lhs GHC], a Haskell compiler (literate latex style) ([http://www.haskell.org/ghc/ home]) |
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+ | |||

+ | * [http://darcs.augustsson.net/Darcs/Djinn/Djinn/LJT.hs Djinn], a theorem prover ([http://darcs.augustsson.net/Darcs/Djinn/ home]) |
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+ | |||

+ | * [http://code.haskell.org/c2hs/src/C2HS/C/Trav.hs c2hs], a C to Haskell interface generator ([https://github.com/haskell/c2hs home]) |
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+ | |||

+ | * [http://code.haskell.org/lambdabot/LBState.hs Lambdabot], an IRC bot ([http://www.haskell.org/haskellwiki/Lambdabot home]) |
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+ | |||

+ | * [http://code.haskell.org/~dons/code/hmp3/Core.hs hmp3], a curses mp3 player |
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+ | |||

+ | * [http://www.haskell.org/haskellwiki/Darcs_repositories More code ...] |
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+ | |||

+ | == Examples == |
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+ | |||

+ | ; [[Tying the Knot]] : An example that illustrates different ways to define recursive data structures. The example defines a simple language (illustrating how to define some recursive structures) and an interpreter for the language (illustrating how to work with the recursive structures). |
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+ | |||

+ | ; [http://members.chello.nl/hjgtuyl/tourdemonad.html A tour of the Haskell Monad functions]: Small usage examples of the basic Haskell monad functions |
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+ | |||

+ | [[Category:Code]] |

## Latest revision as of 09:43, 21 October 2019

To get a feel for what real world Haskell looks like, here are some examples from various popular Haskell projects. To start learning the language, good places to start are Learning Haskell, Haskell in 5 steps, and Books and tutorials.

More code may be found on the wiki.

### Library code

Library code usually differs from application code: it is often highly structured, and documented with haddock, and can be rather optimised. Some instructive examples (syntax highlighting by hscolour):

- A Haskell Prelude.hs, foundational Haskell library (docs)

- Unix.hs, simple unix tools, for beginner Haskellers

- Data.Maybe, the
`Maybe`

type (docs)

- Data.Graph, a graph type (docs)

- Control.Monad, basic monad support (docs)

- QuickCheck, a testing framework (docs)

- PrettyPrint.hs, a pretty printing library (docs)

- Control.Monad.Trans.State.Lazy, a state monad (docs)

- Dfa.lhs, finite automata (literate Bird-style Haskell)

- RedBlackTree.hs, a red-black tree

- Data.Foldable, traversable data structures (docs)

- Data.ByteString, high-performance string type (raw, docs)

- SmallCheck, a testing framework (raw, docs)

### Application code

Code from popular Haskell applications. Such code often makes use of a monadic IO, and sometimes other advanced features such as concurrency:

- hmp3, a curses mp3 player

## Examples

- Tying the Knot
- An example that illustrates different ways to define recursive data structures. The example defines a simple language (illustrating how to define some recursive structures) and an interpreter for the language (illustrating how to work with the recursive structures).

- A tour of the Haskell Monad functions
- Small usage examples of the basic Haskell monad functions