Ur type inference is defined never to deduce the presence of
polymorphism. Rather, polymorphism is always declared explicitly.
In contrast to, say, ML, type inference in Ur is undecidable, hence the
requirement that the program give more annotations.
On 05/29/2013 09:57 AM, David Snider wrote:
Let's say I rewrite that as:
fun zip a b =
case (a, b) of
(a :: as, b :: bs) => (a, b) :: zip as bs
| _ => []
This throws a unification failure until I write:
fun blah () = (zip (1::[]) (2::[]))
At which point the compiler is able to infer the types and all
compiles correctly
Is there some reason that the compiler can't/shouldn't default to:
fun zip [t] [t2] (a : list t) (b : list t2) : list (t * t2) =
case (a, b) of
(a :: as, b :: bs) => (a, b) :: zip as bs
| _ => []
when unification isn't possible?
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