[Haskell-cafe] beginner's problem about lists

Malcolm Wallace Malcolm.Wallace at cs.york.ac.uk
Wed Oct 11 06:40:59 EDT 2006

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).


More information about the Haskell-Cafe mailing list