[Haskell-cafe] Trouble representing a set of flags

[Stefan O'Rear]

On Tue, Feb 06, 2007 at 09:39:22AM +0000, Duncan Coutts wrote:
> On Mon, 2007-02-05 at 19:26 -0800, Stefan O'Rear wrote:
> > I have a structure:
> > 
> > data Attr = Attr { fg :: !Color,
> >                    bg :: !Color,
> >                    bold :: !Bool,
> >                    blink :: !Bool,
> >                    rv :: !Bool,
> >                    halfBright :: !Bool,
> >                    underline :: !Bool
> >                  } deriving(Eq,Show,Ord)
> > 
> > newtype Color = Color Int deriving(Eq,Show,Ord)
> 
> 
> > (Also, GHC seems unable to unbox strict fields that are newtypes.  Can
> > this be done, or should I abandon type safety and use type synonyms?)
> 
> You have to tell GHC that you want fields to be unboxed (this is because
> it's not always an optimisation). You can either do it for all strict
> fields in the whole module by using the -funbox-strict-fields flag, or
> on a per field basis with:
> 
> data Attr = Attr { fg :: {-# UNPACK #-} !Color,
>                    bg :: {-# UNPACK #-} !Color,
>                    ...

I was using -funbox-strict-fields, it was a reporting bug.  Sorry.

Stefan