Hoogle

A Haskell API search engine, written by NeilMitchell. It allows you to search by either name, or by approximate type signature. An article is being written for TheMonadReader, which will include some technical details.

How to use Hoogle

The web interface: http://haskell.org/hoogle
The LambdaBot plugin, @hoogle and @hoogle+
Download the source with CVS: http://sourceforge.net/cvs/?group_id=143787
Download a command line version (yet to be released, but get the source and compile it yourself)
A Mac OS X version (unreleased yet, but it does exist)

Examples

If you wanted to search for the standard prelude function map, you could type into the search any one of:

map 
(a -> b) -> [a] -> [b]
(a -> a) -> [a] -> [a]
(Int -> Bool) -> [Int] -> [Bool]
[a] -> (a -> b) -> [b]

Todo

Admin

Write a website build script
get XHoogle in the repo

Short Term

i.e. before Hoogle3 goes public

Fix all parse errors, prove with a test

-> a
Monad m => Monad m => (a -> m r -> m r) -> r -> [a] -> m r

Regression tests for hoogle
You cannot search for certain keywords, i.e. @, because it is not a recognised lex symbol
Add comment characters, --, {- and -} to the list of symbols.
Add links to this wiki from hoogle.
Add a contact address - maybe: copyright Neil Mitchell - source code - wiki page - report bad search - contact me
Case sensitive search - if searching Map, then Map should come before map.
Put back more detailed information about the Prelude functions.

Medium Term

Parameterise out by package, i.e. split off OpenGL
Compile with Yhc and distribute
Write GTK front end
Firefox/Mozilla plugin
Multiword search? power set
Dehack the Score program
Multiparameter type classes

Long Term

Integration with Cabal
Integration with http://darcs.augustsson.net/Darcs/Djinn
Integration with lambdabot @where and @fact

Hoogle Suggest

People often type to, instead of ->
Numeric literals
Concepts? tuple, random, monads etc.

Bad Searches

(a -> b) -> ([a] -> [b]) -- should find map
@hoogle Data.?IntMap.?IntMap a -> [a] -- badly kills the module names

Higher Kinds

The following searches are all wrong because Hoogle doesn't understand higher kinds, i.e. Monad's.

Functor f => (a -> b) -> f a -> f b -- should find fmap
Monad m => [m a] -> m [a] -- should find sequence
(Monad m) => m (m a) -> m a -- should find join