Mauricio
I'm trying, without success, to understand the difference between existencial quantification and polymorphic datatypes.
Polymorphic types are universally quantified; so id:: forall t. t -> t means that id works for every type t. If haskell had a symbol for existential quantification, hid:: exists t. t -> t would mean that hid only works on some type t, but it doesn't say what it is (so you could only ever apply hid to undefined.
Can you give me a hint
Because being on the left of an arrow works something like negation, a type like (exists t. t -> t) -> bool can be written as forall t . (t -> t) -> bool -- Jón Fairbairn Jon.Fairbairn@cl.cam.ac.uk http://www.chaos.org.uk/~jf/Stuff-I-dont-want.html (updated 2008-04-26)