[GHC] #11350: Allow visible type application in patterns

[GHC]

#11350: Allow visible type application in patterns
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        Reporter:  Iceland_jack      |                Owner:  (none)
            Type:  feature request   |               Status:  new
        Priority:  normal            |            Milestone:
       Component:  Compiler          |              Version:  8.1
      Resolution:                    |             Keywords:
                                     |  TypeApplications PatternSynonyms
Operating System:  Unknown/Multiple  |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  None/Unknown      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:  #11385, #13159,   |  Differential Rev(s):
  #13158                             |
       Wiki Page:                    |
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Comment (by Iceland_jack):

 Using the types from
 [https://github.com/goldfirere/glambda/blob/master/src/Language/Glambda/Type.hs
 Glambda], can we use this to implement

 {{{#!hs
 refineTy_ :: Ty -> (forall ty. ITy ty => Proxy ty -> r) -> r
 refineTy_ IntTy     k = k @Int  Proxy
 refineTy_ BoolTy    k = k @Bool Proxy
 refineTy_ (Arr a b) k =
   refineTy a $ \(Proxy :: Proxy a_ty) ->
   refineTy a $ \(Proxy :: Proxy b_ty) ->
     k @(a_ty -> b_ty) Proxy
 }}}

 without `Proxy ty`?

 {{{#!hs
 refineTy_ :: Ty -> (forall ty. ITy ty => r) -> r
 refineTy_ IntTy     k = k @Int
 refineTy_ BoolTy    k = k @Bool
 refineTy_ (Arr a b) k =
   refineTy a $ \@a_ty ->
   refineTy a $ \@b_ty ->
     k @(a_ty -> b_ty)
 }}}

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/11350#comment:17>
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