Newtype type class with compiler generated instances

Define a Newtype class, autmatically generating instances

class Newtype n where
  type O n :: Type

  pack   :: O n -> n
  unpack :: n   -> O n

as defined in Conal's Generic parallel functional programming but also found in the newtype and lens packages.

I run into this class every once in a while

Trac metadata

Trac field	Value
Version	8.0.1
Type	FeatureRequest
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Compiler
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