At Sat, 18 Feb 2012 21:39:33 -0600, Robby Findler wrote: > > Still, good to > > know. I didn't think of using Typed Racket like that. > > > > I should mention that this is the best method I've found so far: > > > > (: float->int (Float -> Integer)) > > (define (float->int x) > > (floor (inexact->exact (floor x)))) ; both floors are necessary > > Why is the second floor necessary? Just for the type system or are > there inexact integers that become exact non-integers?
Yes. The inner `floor' produces a float that represents an integer. TR doesn't distinguish them from other floats, so the result of `inexact->exact' is of type `Exact-Rational'. The outer floor takes it to the type `Integer'. From the type system's perspective, the inner floor is not necessary. However, leaving it out may cause `inexact->exact' to return fractions in some cases, which would be bad performance-wise. From Racket's point of view, the outer floor is not necessary, since `inexact->exact' will always return integers, on which `floor' is the identity. Vincent ____________________ Racket Users list: http://lists.racket-lang.org/users
