Is there something available which can answer questions like this - what all packages on Hackage export "Data.List" module? Another useful question could be - what all packages export symbol named 'x'? Hackage search or hoogle are not helpful in providing a precise answer to these.

I am assuming that related functionality usually lands up in the same part of the module namespace. This fact can help us in discovering related or alternative packages or functions available in a given area. For example when I am looking for list related functions I can search for who all exports "Data.List".

I guess creating such an index should not be difficult. All the necessary information is available in the packages' .cabal files, we just need to extract it and create a module name to package name index.

-harendra