Re: [GHC] #13408: Consider inferring a higher-rank kind for type synonyms

27 Feb 2019

      #13408: Consider inferring a higher-rank kind for type synonyms
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        Reporter:  goldfire          |                Owner:  (none)
            Type:  feature request   |               Status:  new
        Priority:  normal            |            Milestone:  8.10.1
       Component:  Compiler          |              Version:  8.0.1
      Resolution:                    |             Keywords:  TypeInType,
                                     |  VisibleDependentQuantification
Operating System:  Unknown/Multiple  |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  None/Unknown      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
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Changes (by RyanGlScott):

 * keywords:  TypeInType => TypeInType, VisibleDependentQuantification

Comment:

 Visible dependent quantification provides another workaround for this
 issue:

 {{{#!hs
 {-# LANGUAGE DataKinds #-}
 {-# LANGUAGE PolyKinds #-}
 {-# LANGUAGE RankNTypes #-}
 module Foo where

 import Data.Kind

 data A :: Type -> Type
 data B a :: A a -> Type
 type C = (B :: forall a -> A a -> Type)
 }}}

 This workaround is mildly more tolerable, since it doesn't rely on
 `ImpredicativeTypes`.

-- 
Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/13408#comment:13
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