Hoogle 4 New Features

I'm still developing Hoogle 4, and there are many things that don't work (such as searching for types and the web version). However, it's starting to come together, and I'm beginning to implement new features that aren't in Hoogle 3. Today I've implemented two useful features.

Multi Word Text Search

In Hoogle 3, if you entered "is just" it would be treated as a type search, exactly the same as "m a". Now, it will search for "is" and search for "just" and intersect the results. This seems to be something that people often try, so hopefully will make Hoogle more intuitive.

Intelligent Suggestions

Hoogle 3 tries to give suggestions, for example if I search for "a -> maybe a" it will helpfully suggest "a -> Maybe a". Unfortunately it's not that clever. If your search term contains a type variable (starting with a lower-case letter), which is more than one letter, it will suggest you try the capitalised version. For example, "(fst,snd) -> snd" will suggest "(Fst,Snd) -> Snd", which isn't very helpful.

The new mechanism uses knowledge about the types, arities and constructors present in the Hoogle database. Some examples:

"Just a -> a"  ===> "Maybe a -> a"
"a -> Maybe"   ===> "a -> Maybe b"
"a -> MayBe a" ===> "a -> Maybe a"
"a -> maybe a" ===> "a -> Maybe a"

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