[Haskell-cafe] Lazy Lists and IO

[Andrew Coppin]

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?