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?
On 05/28/2013 09:26 AM, Adam Chlipala wrote:
On 05/28/2013 06:15 AM, David Snider wrote:
In standard ML you can write
fun zip _ _ = []
| zip (a::as) (b::bs) = (a,b) :: (zip as bs)
What would be the Ur equivalent of this kind of pattern matching?
I'm assuming your code has a bug in the ordering of the patterns,
which I fix below.
fun zip [t] (a : list t) (b : list t) : list (t * t) =
case (a, b) of
(a :: as, b :: bs) => (a, b) :: zip as bs
| _ => []
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