Come to think of it, ifdecap is a bit paradoxical.... If it's used to destructure argument lists, then it'll be recursive upon itself over and over and probably never get anywhere. (It needs to return two values somehow, which means either the caller or a CPS-style callback will need to destructure those values. I don't plan to look for a multiple-value-return-esque solution.) I guess the built-in argument list type will need some kind of hardwired treatment just like the built-in function type.