Standalone Interface Bindings

Hello again. In Interfaces - Part 4, I talked through the basic interface support which looks mostly like C# and other popular languages, with a little more functionality. You can declare an interface, and when you declare a class, you can say that it implements that interface. Now for some things that are not like what is available in popular languages.

One of the big things about Haskell type classes is that they don't work like that. They don't require you to include the interface reference when declaring your type. Let's look back at the example from Part 4:

convertible to string :> interface {
  (this) => string;
}

Cow :> cow :< convertible to string {
  (this) => string { "moo..." }
}

(x: convertible to string) speak => void {
  print x;
}

entrypoint => void {
  cow speak;
}

The second declaration is our type declaration for Cow, along with our inline interface binding. With today's check-in you can do standalone interface binding as well:

convertible to string :> interface {
  (this) => string;
}

Cow :> cow { }

Cow :< convertible to string {
  (this) => string { "moo..." }
}

(x: convertible to string) speak => void {
  print x;
}

entrypoint => void {
  cow speak;
}

Here, Cow is tied to convertible to string in its own standalone interface binding declaration, along with the implementation for that interface. This looks and acts a lot more like Haskell type classes. With this, you can take classes defined in some other library and adapt them to your interfaces (or vice versa).