[Haskell-cafe] Re: Scraping boilerplate deriving?

[Kevin Jardine]

I supposed the simple solution might be CPP:

#define defObj(NAME) newtype NAME = NAME Obj deriving (A,B,C,D)

and then use

defObj (MyType)

I have heard some people, however, say that CPP macros are horrible in
Haskell, so is there a better solution?

Kevin

On Sep 14, 10:34 am, Miguel Mitrofanov <miguelim... at yandex.ru> wrote:
>   Sorry, got stupid today. Won't help.
>
> 14.09.2010 12:29, Miguel Mitrofanov пишет:
>
> >  class (A x, B x, C x, D x) => U x
>
> > ?
>
> > 14.09.2010 12:24, Kevin Jardine пишет:
> >> 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?
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