[GHC] #15961: TH 'Lift' instance for 'NonEmpty'

[GHC]

#15961: TH 'Lift' instance for 'NonEmpty'
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           Reporter:  fr33domlover   |             Owner:  (none)
               Type:  feature        |            Status:  new
  request                            |
           Priority:  normal         |         Milestone:  8.6.3
          Component:  Template       |           Version:  8.6.2
  Haskell                            |
           Keywords:  lift,          |  Operating System:  Unknown/Multiple
  instance, nonempty                 |
       Architecture:                 |   Type of failure:  Other
  Unknown/Multiple                   |
          Test Case:                 |        Blocked By:
           Blocking:                 |   Related Tickets:
Differential Rev(s):                 |         Wiki Page:
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 I was using `deriving Lift` on a data type and the `DeriveLift` extension:

 {{{#!hs
 import Data.List.NonEmpty
 import Language.Haskell.TH

 data T = T (NonEmpty String) Int
 }}}

 and I noticed I couldn't get an automatic instance because `NonEmpty`
 doesn't have a `Lift` instance. I'm wondering if an instance can be added
 to the `template-haskell` package (or elsewhere if that isn't the right
 place? I'm assuming it is because `NonEmpty` is in `base` now)

 Since `NonEmpty` has a `Data` instance, I suppose the following would be
 enough?

 {{{#!hs
 instance Data a => Lift (NonEmpty a)
 }}}

 And without using `Data` it could be:

 {{{#!hs
 nonemptyConName :: Name
 nonemptyConName = mkNameG DataName "base" "Data.List.NonEmpty" ":|"

 instance Lift a => Lift (NonEmpty a) where
     lift (x :| xs) = do
         x' <- lift x
         xs' <- traverse lift xs
         return $ ConE nonemptyConName `AppE` x' `AppE` xs'
 }}}

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/15961>
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