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

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+-%3E+b%29+-%3E+%5Bb%5D 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.