13 Feb
2009
13 Feb
'09
5:03 a.m.
On Fri, Feb 13, 2009 at 7:56 AM, Daniel Fischer
You need the forall a to bring the type variable a into scope. Without it, the a in
arr0 <- (newListArray (0, n) xs :: IO (IOArray Int a))
would be implicitly universally quantified, too, and you would say that all elements of xs had type (forall b. b), which means all are _|_. Having brought the a from permute's type signature into scope, the a in the above line is the *same* a as the one in permute's type signature.
Whoops, sorry about that, didn't see that ScopedTypeVariables was active. :) -- Felipe.