From the webpage:
Hoogle is a Haskell API search engine, which allows you to search many standard Haskell libraries by either function name, or by approximate type signature.
[example searches omitted]
The Hoogle manual contains more details, including further details on search queries, how to install Hoogle as a command line application and how to integrate Hoogle with Firefox/Emacs/Vim etc.
Just in case you missed the reference in our post on Scalex (a similar interface for Scala).
Oh, Hoogle enables searching by “…function name, or by approximate type signature.”
What other searches you would like to perform?
How would you implement those searches? (by what kind of indexing including software to be used) Care to do that as a project to contribute back to the community?
Do you think topic maps could improve this resource? In what way?