[Haskell-cafe] Scraping boilerplate deriving?

[Kevin Jardine]

I have a set of wrapper newtypes that are always of the same format:

newtype MyType = MyType Obj deriving (A,B,C,D)

where Obj, A, B, C, and D are always the same. Only MyType varies.

A, B, C, and D are automagically derived by GHC using the

{-# LANGUAGE GeneralizedNewtypeDeriving #-}

feature.

I would like to use some macro system (perhaps Template Haskell?) to
reduce this to something like

defObj MyType

I've read through some Template Haskell documentation and examples,
but I find it intimidatingly hard to follow. Does anyone has some code
suggestions or pointers to something similar?

Alternatively, is there any way in standard Haskell to define some
kind of union class:

U = (A, B, C, D)

and then using

newtype MyType = MyType Obj deriving U

which would at least be shorter?