Annotated types

[ktec]

Hi, firstly thanks for an excellent library!

I have discovered that annotated types are not validated by the checker correctly.

I have reduced it down to the following test:

type = {:ann_type, 0, [{:var, 0, :annotation}, {:atom, 0, :atom}]}
term = :atom

typespec = Code.Typespec.type_to_quoted(type) |> Macro.to_string()

assert typespec == "ann_type(annotation, :atom) :: 0"
assert RTypes.Checker.check(term, type) == :ok

=> {:error, [term: :atom, message: "term does not conform to type", types: [{:ann_type, 0, [{:var, 0, :annotation}, {:atom, 0, :atom}]}], ctx: []]}

I'm happy to attempt a fix, but I wanted to check [sic] whether adding another function head to checker.ex is the right approach. Something like this:

  ## annotations
  defp check(term, {:ann_type, _, [{:var, _, annotation}, typ]}, ctx) do
    case check(term, typ, ctx) do
      :ok ->
        :ok

      {:error, _} ->
        {:error,
         term: term,
         message: "term does not match annotated #{annotation} type",
         types: [typ],
         ctx: ctx}
    end
  end

I've got this in a branch, if you're happy with it, or have suggestions to improve?

[d2km]

Thanks for submitting the issue. The PR looks good to me, but I'd prefer an individual PRs for unrelated changes. Please let me know if you are happy to do so.