Could someone give me a motivating example for what this enables?
If there is such in the paper, a link to the paper is fine.
On Sat, Aug 4, 2018 at 10:27 AM, Joachim Breitner
Hi,
can we have an additional nod by someone who is not an author of the corresponding paper?
Also, I updated the proposal to answer the disambiguation with as- patterns: https://github.com/ghc-proposals/ghc-proposals/pull/126/commits/12d64105b097... And I would like a second pair of eyes there, as this choice blocks us from in the future allowing patterns on both sides on @, i.e. something like
Just (_ :_) @ (fun -> True) @ x
because
Nothing @ a
would be ambiguous.
Cheers, Joachim
Am Donnerstag, den 26.07.2018, 11:08 +0300 schrieb Iavor Diatchki:
let's also start the discussion on feature request 126. The idea here is that we allow the @ notation for explicit type applications to also be used on constructors in patterns. Using @ with a constructor in a pattern has the same meaning as it does it an expression: the provided type is used to instantiate the corresponding type parameter of the constructor. If the type contains variables, those are treated in the same way as in #128, where "unbound" variables name the matching types. Here are some examples:
f1 (Just @Int x) = x -- This has type `Maybe Int -> Int`
f2 (Just @[a] x) = x == "c" -- `a` is an alias for `Char`
f3 (SomeException @e ex) = ... -- `e` is a name for the existentially hidden exception type
Overall I think that is a simple and natural extension to the way @ already works, and I propose that we accept it.
Thoughts?
-Iavor
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