In haskell and all ML children, when you pass too few arguments to a fn, it would just yield a curried version. Of course, they have static type systems to reduce errors caused by passing too few arguments. but I guess Arc's goal is to be good for quick prototyping, not good at elimating run-time errors...
That is one of the features of Haskell I really like. I'm not sure of all the implications for attempting it with Arc, but if it's possible to do it well, I think it's worth the research.