Unboxed Vectors of newtype'd values

Andres Löh andres at well-typed.com
Tue Jun 5 21:54:05 CEST 2012

Hi Bryan.

> Yes, I (and I assume Bas) want generalised newtype deriving to work, but it
> doesn't.
> I want to write something very simple:
> {-# LANGUAGE GeneralizedNewtypeDeriving #-}
> newtype Foo = Foo Int
>     deriving (Eq, Show, Unbox)
> But with the above, GHC says:
>     No instances for (M.MVector MVector Foo, G.Vector Vector Foo)
>       arising from the 'deriving' clause of a data type declaration

Yes, because these are superclasses of Unbox. So can't you simply say this:

> newtype Foo = Foo Int
>   deriving (Eq, Show, Unbox, M.MVector MVector, G.Vector Vector)



Andres Löh, Haskell Consultant
Well-Typed LLP, http://www.well-typed.com

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