About 2 months ago Frederik Eaton posted "HsMan" to the ghc list, a program that with one command line could look up the documentation for a function. Now Hoogle 4 has that feature :)
$ hoogle +filepath combine /info /doc
System.FilePath.Version_0_09.combine :: FilePath -> FilePath -> FilePath
Combine two paths, if the right path isAbsolute, then it returns the second.
Posix: combine "/" "test" == "/test"
Posix: combine "home" "bob" == "home/bob"
Windows: combine "home" "bob" == "home\\bob"
What the above says is search the filepath module for the name combine, and when you find it, with the one that ranks best, display the haddock entry for it (info) and a link to further documentation (doc)
It was a reasonable amount of work to add, but there is a good reason for adding this feature, which will become clear when Hoogle 4 web version is relased :)