[GHC] #8460: Annotation reification with types in TH

[GHC]

#8460: Annotation reification with types in TH
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        Reporter:  errge       |            Owner:
            Type:  feature     |           Status:  patch
  request                      |        Milestone:  7.10.1
        Priority:  normal      |          Version:  7.7
       Component:  Template    |         Keywords:
  Haskell                      |     Architecture:  Unknown/Multiple
      Resolution:              |       Difficulty:  Easy (less than 1 hour)
Operating System:              |       Blocked By:
  Unknown/Multiple             |  Related Tickets:  #8397
 Type of failure:              |
  None/Unknown                 |
       Test Case:              |
        Blocking:              |
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Comment (by monoidal):

 I like `liftTyped`. I would go even further and add it to the `Lift`
 class:

 {{{
 class Lift t where
   lift :: t -> Q Exp
   liftTyped :: t -> Q (TExp t)
   lift = unTypeQ . liftTyped
   liftTyped = unsafeTExpCoerce . lift
   {-# MINIMAL lift | liftTyped #-}
 }}}

 Now, when you write an instance of `Lift`

 {{{
 data A = A

 instance Lift A where
   liftTyped A = [e|| A ||]
 }}}

 the compiler will detect if you mistakenly use a different type in the
 `[e|| ... ||]` brackets.

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/8460#comment:4>
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