Re: [Haskell-cafe] beginner's problem about lists

On Wed, Oct 11, 2006 at 11:40:59AM +0100, Malcolm Wallace wrote:

To: haskell-cafe@haskell.org From: Malcolm Wallace Date: Wed, 11 Oct 2006 11:40:59 +0100 Subject: Re: [Haskell-cafe] beginner's problem about lists

ihope wrote:

...

It's possible to make both "infinite list" and "finite list" datatypes:

data Inf a = InfCons a (Inf a) data Fin a = FinCons a !(Fin a) | FinNil

At least, I think the Fin type there has to be finite...

No, your Fin type can also hold infinite values. The strictness annotation on the (Fin a) component merely ensures that the tail exists to one constructor's depth (Head Normal Form). It does not force strictness all the way down (full Normal Form).

let q = FinCons 3 q in case q of FinCons i _ -> i ==> _|_ does that contradict, or did i just not understand what you are saying? matthias