This change adds a new primitive Implements which changes interface
implementations from being implicit to being explicit. Going forward,
users will have to declare (implements <interface> <implementation>) to
explicitly add a function to an interface. This provides two benefits:
- Prevents unwitting name clashes. Previously, if one defined a function
that happened to have the same name as an interface, it was
automatically assumed the function implemented that interface when this
is not always the intention, especially in large programs.
- Name flexibility. One can now implement an interface with a function
that has a different name than the interface, which allows for greater
flexibility.
I've updated core to make the necessary calls to the new primitive.
Since str and copy are derived automatically for types, we treat these
functions as a special case and auto-implement the interfaces.
