Jason Dusek wrote:
Why is `Int` used in so many places where it is semantically wrong? Not just here but also in list indexing... Indices/offsets can only be positive and I can't see any good reason to waste half the address space -- yet we encounter this problem over and over again.
I think history is the biggest culprit. Haskell98 doesn't ship with Nat and Natural types, so Int and Integer are used instead. And then the Word* types come around for bit bashing. Another big culprit is that this is one of the places where Haskell gives a nod to performance. Many Prelude functions like take, drop, and (!!) should accept any Natural. Failing that, they should accept Integer and do the right thing for negatives. But most of the time an Int is sufficient, and that's what they take; this increases CPU performance, but more importantly it increases programmer performance since they don't need to write All Those Conversion Functions(tm). Though programmer performance suffers when an unbounded type is actually required, or when negatives aren't handled correctly. The haskell' committee is considering adding a Nat or Natural type, so history may eventually be corrected. However, in order to deal with them in an, er, natural way the numeric typeclass hierarchy needs fixing. At the very least we'd want to separate (+) and (*) from (-), negate, abs, and signum so that we have a class for Nat and Natural that doesn't have partial functions. A safe version of (-) would be nice, though it's an open question whether x-(x+y) should be 0 or Nothing[1]. It's also unclear what should happen to fromInteger: do we have fromNatural be a subfunction of it, or do we desugar negative literals with negate and fromNatural and drop fromInteger entirely? [1] My vote would be for Nothing so that we don't loose the information about whether the two operands are equal. Though this has the unfortunate side effect of requiring more plumbing. We could always offer both variants, so that clients who use subtraction and equality comparisons together frequently can use the Maybe version and those who want the other mathematical function can use it instead. -- Live well, ~wren