Make the Template Haskell class Lift work over typed expressions

At the moment we have the Lift class in TH:

class Lift t where
  lift :: t -> Q Exp

But that loses type information. What we want is this:

Lift t where
  typedLift :: t -> Q (TExp t)

lift :: Lift t => t -> Q Exp
lift = fmap unType . typedLift

Otherwise, when you want the typed version, people resort to unsafe-coerce operations, which are entirely unnecessary.

See this thread on the libraries list.

Trac metadata

Trac field	Value
Version	8.2.2
Type	FeatureRequest
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Template Haskell
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