Allow defmulti without expected type

Problem

defmulti expressions need an expected type at the moment. This is annoying and we can do better.

This should type check without issues.

(defmulti f identity)

Solution

Remove the restriction on a MultiFn requiring an expected type. This raises the question of how to infer the type of a multimethod based only on its dispatch function.

Here is the new scheme:

If the dispatch function is a function type

[b ... b -> c]

the entire multimethod is of type

[b ... b -> Any]

That is, infer the type of the dispatch function, and replace the return types with Any.

eg.

(defmulti f identity)

Dispatch function is of type

(All [x] [x -> x :object {:id 0}])

Multimethod annotated as:

(All [x] [x -> Any])

Filters and objects should be deleted from the dispatch function to generate the multimethod annotation.

Pull request: 83
Commit:
Version: