On Wednesday 23 Jun 2004 10:46 am, MR K P SCHUPKE wrote:

...

f (i:is) = even i : f is f e = e

This still makes perfect sense to me... you see the let binding:

let e@[] = e

has no additional information about the type of [] so it must be fully polymorphic.

if the function binding we know typeOf e == typeOf (i:is) and that i is a member of the class Integral (from the application of even) As we always take the most precise available type we end up with

forall a. Integral a => [a]

as the type for 'e'... Now Bool is not a member of Integral so it is a type error!

It's only a type error because Haskell currently defines it as such. It's not a type error in the sense that programs which were typed the way I suggest would cause a runtime error. As for the issue of resolving overloading ambiguities, there is indeed a distinction between an empty list of Ints and an empty list of Bools. There should not be IMO. IIRC this issue is what lead Fergus Henderson to describe what what I was proposing as a hack, all those years ago. Though personally I regard it as evidence that Haskells overloading mechanisms, as currently implemented, are a hack :-) Regards -- Adrian Hey