I've noticed a bug in the error message that is provided when you are in uncurried mode and you provide a curried function to an uncurried signature:

module Foo: { let get: (Js.Dict.t<'a>, Js.Dict.key) => option<'a> } = { let get = Js.Dict.get }

this yields the following error:

[E] Line 3, column 4: Signature mismatch: ... Values do not match: let get: (Js.Dict.t<'a>, Js.Dict.key) => option<'a> is not included in let get: (Js.Dict.t<'a>, Js.Dict.key) => option<'a> playground.res:2:3-53: Expected declaration playground.res:4:7-9: Actual declaration 

Tested in v11.0.0-rc.3 (playground link).

Interestingly enough, it shows the correct error message when inlining the signature:

let get: (Js.Dict.t<'a>, Js.Dict.key) => option<'a> = Js.Dict.get

This function is a curried function where an uncurried function is expected 

Originally got suspicious about this bug from this post on the forum.