Re: [GHC] #12245: Deriving Data at higher kinds

31 Jan 2018

      #12245: Deriving Data at higher kinds
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        Reporter:  simonpj           |                Owner:  simonpj
            Type:  bug               |               Status:  closed
        Priority:  normal            |            Milestone:
       Component:  Compiler          |              Version:  8.0.1
      Resolution:  fixed             |             Keywords:
                                     |  QuantifiedConstraints
Operating System:  Unknown/Multiple  |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  None/Unknown      |            Test Case:
                                     |  deriving/should_compile/T12245
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
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Comment (by Iceland_jack):

 With [https://phabricator.haskell.org/D4353 D4353] this can be written as:

 {{{#!hs
 {-# Language QuantifiedConstraints #-}
 {-# Language StandaloneDeriving #-}
 {-# Language DeriveDataTypeable #-}
 {-# Language FlexibleInstances #-}
 {-# Language UndecidableInstances #-}
 {-# Language KindSignatures #-}
 {-# Language RankNTypes #-}
 {-# Language ConstraintKinds #-}

 import Data.Data (Data)
 import Data.Typeable
 import Data.Kind (Constraint)

 data Foo f = Foo (f Bool) (f Int)

 type LevelUp cls f = (forall xx. cls xx => cls (f xx) :: Constraint)

 deriving instance (Typeable f, LevelUp Data f) => Data (Foo f)
 }}}

 Can this ticket be closed?

-- 
Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/12245#comment:7
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