It's not hard to write a macro in Arc/Nu that uses Racket's case-lambda, and in fact I had a semi-working version, but I gave that up when I started work on Nulan.
Unlike Arc, Nulan doesn't have optional args, so you have to use arity overloading:
$def foo
X Y -> X + Y # 2 argument version
X -> (foo X 10) # 1 argument version: default for Y is 10
Though I suppose it shouldn't be too hard to write a pattern matcher that supports optional args... something like this:
$def foo
X (opt Y 10) -> X + Y
In this case, "opt" is an object that has a %pattern-match type, which means users can write their own pattern matchers, unlike in Arc where it's all hardcoded.
