On 1 October 2010 15:27, Henning Thielemann <lemm...@henning-thielemann.de> wrote: > > Given the following code, that is accepted by GHC: > >> data Exist = forall a. Exist a >> >> exist :: Exist >> exist = Exist undefined > > What type has the 'undefined' ?
I think its type is `a'. > > So far I assumed that at runtime all objects have a concrete type. This > seems not to be true. Consider the following program: main = putStrLn $ show $ length [undefined :: a,undefined :: b] A concrete type of the element in list doesn't need to be determined at runtime, or any time. a unifies with b, and that unifies with x in length :: [x] -> Int. _______________________________________________ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
