Example code

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

• List.hs, the standard list library (docs)

• Maybe.hs, the Maybe type (docs)

• Map.hs, the standard finite map (docs)

• Graph.hs, a graph type (docs)

• Monad.hs, basic monad support (docs)

• QuickCheck, a testing framework (docs)

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

• State.hs, a state monad (docs)
• Dfa.lhs, finite automata (literate Bird-style Haskell)

• [1], a red-black tree
• Foldable.hs, traversable data structures (docs)

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

• [2], a testing framework (raw, docs)

• More code ...

Application code

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

• Pugs, a perl6 implementation (home)

• Yi, a text editor, (home, raw, [http://hackage.haskell.org/package/yi doc)
• cpphs, an implementation of the C preprocessor (home)

• GHC, a Haskell compiler (literate latex style) (home)

• Djinn, a theorem prover (home)

• c2hs, a C to Haskell interface generator (home)

• Lambdabot, an IRC bot (home)

• hmp3, a curses mp3 player

• More code ...

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