12 Jul
2007
12 Jul
'07
2:03 p.m.
Jonathan Cast wrote:
On Wednesday 11 July 2007, Chaddaï Fouché wrote:
Is there something I misunderstood in the exchange ?
Yeah. The reference to the "lazy natural type", which is:
data Nat = Zero | Succ Nat deriving (Eq, Ord, Read, Show)
instance Num Nat where fromInteger 0 = Zero fromInteger (n + 1) = Succ (fromInteger n) etc.
then genericLength xn > n does exactly what Andrew wants, when n :: Nat.
Wow. Show me a simple problem, and some Haskeller somewhere will find a completely unexpected way to solve it... LOL! OTOH, doesn't that just mean that Nat is itself a degenerate list, and genericList is just converting one list to another, and the Ord instance for Nat is doing the short-cut stuff?