It is a special search engine for Haskell libraries. For example, if I want the `map` function but don't know what it's called (or what library it's in) I can search for its type signature, which must be something like `[a] -> (a -> b) -> [b]`. Hoogle finds exactly what I'm looking for: https://www.haskell.org/hoogle/?hoogle=%5Ba%5D+-%3E+%28a+-%3...

Note that this is true even though I reversed the argument order. It does fuzzy-matching of some sort. It will also help if you know the name of the function, since it searches those, too.

Yes, it's a special search engine: https://www.haskell.org/hoogle/

You don't search for words in the documentation etc., but enter the type of the function you want. This often works pretty well.

FPComplete's Hoogle is a bit more complete: https://www.fpcomplete.com/hoogle

It's good overall but sometimes the ranking is weird. For example, if you search for "ByteString", what you'd expect is only the #3 hit.

For beginners who are likely to be searching for core libraries, the other Hoogle might be more useful.