[Template-haskell] Reification of top level variables - was: Re: Problem with Labelled Fields

[Eric Offermann]

> What you will actually
> get is the code for applying "c_succ" to lift c (it is lifted as it is
> an argument to the function). However, lifting c needs to use this
> instance again so loops.
> 
> Ian

Ian, thanks a lot for pointing that out. This leads me to the following
modification:

{- spliceC.hs -}
module spliceC where

import Language.Haskell.THSyntax

data C a = C
  {c_succ :: a -> a
  ,c_pred :: a -> a
  }

instance Lift (C a) where
  lift c =
    recCon "C"
      [fieldExp "c_succ" [| c_succ $(var "sampleC") |]
      ,fieldExp "c_pred" [| c_pred $(var "sampleC") |]
      ]

c_succS :: C a -> ExpQ
c_succS c = [| \ a -> c_succ c a |]

sampleC :: C Int
sampleC = C
  {c_succ = \ n -> n + 1
  ,c_pred = \ n -> n - 1
  }

Thus, the possibility of using a "reifyVar c :: Q String" in the instance of
lift c yielding the original name of c would be useful to keep the instance
decleration generic. Any hint on implementing that?

Thanks,
Eric

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