Hi
I don't know if it is theoretically sound or possible, but
it would be helpful, if the typing of match-with statements with polymorphic
variants was able to remove one or more variants from the "catch-all" cases
In the following code, it would mean that three_is_a_lot would be typed like
three_is_a_lot_2 without having to write all the cases.
# let how_much = function
| 1 -> `One
| 2 -> `Two
| 3 -> `Three
| n -> `A_lot;;
val how_much : int -> [> `A_lot | `One | `Three | `Two ] = <fun>
# let three_is_a_lot x =
match how_much x with
| `Three -> `A_lot
| any -> any;;
val three_is_a_lot : int -> [> `A_lot | `One | `Three | `Two ] = <fun>
# let three_is_a_lot_2 x =
match how_much x with
| `Three -> `A_lot
| `One | `Two | `A_lot as any -> any;;
val three_is_a_lot_2 : int -> [> `A_lot | `One | `Two ] = <fun>
The practical use-case for us is that we use polymorphic variants to encode
"semantic" errors in an Error/Result monad.
What does the list think?
Cheers,
Sebastien
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