[Haskell-cafe] beginner's problem about lists

[Malcolm Wallace]

ihope <ihope127 at gmail.com> 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).

Regards,
    Malcolm