On Tue, Sep 14, 2010 at 10:24, Kevin Jardine wrote:
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?
This works in TH:
[d|newtype Blah = Blah Int deriving (Num,Show,Eq)|]
But the parameterized variations on this theme do not:
derive1 name = [d|newtype $name = Blah Int deriving (Num,Show,Eq)|] Malformed head of type or class declaration
derive2 name = [d|newtype Blah = $name Int deriving (Num,Show,Eq)|] parse error in data/newtype declaration
I think it has something to do with the type of the splice. Perhaps you can look into further: http://www.haskell.org/ghc/docs/6.12.2/html/users_guide/template-haskell.htm... Sean