interface IFoo<T> {
    associatedtype Output;
    func foo(other: T) -> Output;
}

struct Ant {};
struct Bat {};
struct Cat {};
struct Dog {};
struct Ewe {};
struct Fox {};
struct Gnu {};

extension Ant: IFoo<Bat> {
    typedef Cat Output;
    func foo(other: Bat) -> Cat { return Cat(); }
}
extension Ant: IFoo<Dog> {
    typedef Ewe Output;
    func foo(other: Dog) -> Ewe { return Ewe(); }
}
extension Ant: IFoo<Fox> {
    typedef Gnu Output;
    func foo(other: Fox) -> Gnu { return Gnu(); }
}

problem.slang(18): error 38100: type 'Ant' does not provide required interface member 'foo'
extension Ant: IFoo<Dog> {
               ^~~~
problem.slang(3): note: see interface requirement declaration of 'foo'
    func foo(other: T) -> Output;
         ^~~
problem.slang(22): error 38100: type 'Ant' does not provide required interface member 'foo'
extension Ant: IFoo<Fox> {
               ^~~~
problem.slang(3): note: see interface requirement declaration of 'foo'
    func foo(other: T) -> Output;
         ^~~