[Haskell-cafe] Scraping boilerplate deriving?

Miguel Mitrofanov miguelimo38 at yandex.ru
Tue Sep 14 04:34:19 EDT 2010


  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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