Searching by type signature is very useful. I think searching by example input and output pairs would be a great addition to Haskell as well, especially for beginners and the base libraries.

A technique I use for poorly documented libraries is searching in github '<some keywords> <optionally library name> language:<language>'. Unfortunately there are some serious limitations in github search, no way escape certain characters.

In short, yes. You give it an example of the types involved. Instead of "hi" -> "HI" you give String -> String.