Re: [Haskell-beginners] Empty list

On Wed, Mar 25, 2015 at 9:03 AM, Brandon Allbery wrote:

On Wed, Mar 25, 2015 at 10:00 AM, Norbert Melzer wrote:

...

You are correct, a list is not a set. A list is a list of things, that can be there multiple times. A set is a set of things, where nothing can be twice. So take a look at Data.Set

Note that this won't actually solve the original problem; Haskell is an implementation of a strongly typed lambda calculus, not of number theory, and Haskell collections cannot (easily) contain elements of different types --- so the empty set is not an element of a set, and the empty list is not an element of a list.

Did you forget a couple of "necessarily"'s? Prelude Data.Set> [] `elem` [[]] True Prelude Data.Set> empty `member` (insert empty empty) True