But that macro, and the whole plumbing behind declaring and checking type classes, just don't have to exist if you make it implicit. It's a lot of added complexity for no gain in power. All you gain is a little type safety - and if you need type safety, Arc (and Lisp in general) is not your language.
I wonder how much type-checking major Lisp libraries really do have. In the dynamically-typed-language libraries I've looked at, there are more or less no type checks. In the Ruby community, they're specifically discouraged, because they limit the power of duck typing.
Yes, but who says it has to be used? In the majority of code, there won't be type checking, but we do want to say something like this:
This function accepts a list of ordinal types
which we can simply put in-code as:
(type-declaration a 'Scanner)
(type-declaration (car a) 'Ordinal)
The point is that the function doesn't specifically accept a list of strings or numbers - it accepts a traversable sequence of anything that can be ordered. The type-declaration thing is just a notation to express that to someone else.
