Re: 2533: Generic functions that take integral arguments should work the same way as their prelude counterparts

Can you examples of both naive definitions and fast definitions of Nat? I'm curious.

Naive:

data Natural' = Zero | Succ Natural'

Fast:

type Nat = Word64

(or Word if you want to retrofit to Haskell-1.5, a.k.a. Haskell98 ;-).

newtype Natural = N Integer -- to be exported abstractly

instance Num Natural where ... N a - N b = let d = a - b in if d >= 0 then N d else error "Illegal Natural subtraction" -- one argument against Num ;-)

subtract (N a) (N b) = let d = a - b in if d >= 0 then Just $ N d else Nothing

.... Wolfram