On Fri, May 28, 2010 at 9:21 PM, Robby Findler <ro...@eecs.northwestern.edu> wrote: >> - [else (loop (- i 1) >> + [else (loop (sub1 i) > > Okay, I'll bite. Why does (- i 1) do something different than (sub1 > i)? Is sub1 overloaded in some useful way that - cannot be? Or is it > something about the constant?
`sub1' has the type, among others, of: (Exact-Positive-Integer -> Exact-Nonnegative-Integer) In this example, `i' (the argument to `loop') has argument type `Exact-Nonnegative-Integer'. But above that line, we've tested that `i' isn't 0. So `i' is an `Exact-Positive-Integer'. So the `sub1' call produces exactly the right type for the call to `loop'. `-' can't have a type that does that, unless we special-case 1. -- sam th sa...@ccs.neu.edu _________________________________________________ For list-related administrative tasks: http://list.cs.brown.edu/mailman/listinfo/plt-dev
