container for different types, avoiding boiler plate

[Hal Daume]

Yes, this is essentially what DynamicMap is....The url i posted before
was wrong...it should have been:

  www.isi.edu/~hdaume/haskell/DynamicMap.hs

 --
 Hal Daume III                                   | hdaume@isi.edu
 "Arrest this man, he talks in maths."           | www.isi.edu/~hdaume


> -----Original Message-----
> From: Markus.Schnell@infineon.com=20
> [mailto:Markus.Schnell@infineon.com]=20
> Sent: Thursday, August 21, 2003 1:58 AM
> To: haskell@haskell.org
> Cc: Hal Daume; ddarius@hotpop.com
> Subject: Re: container for different types, avoiding boiler plate
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> After taking a look at Data.Dynamic I came up with:
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> > data Gender =3D Masc | Fem | Neutr     deriving (Typeable, Show)
> > data Number =3D First | Second | Third deriving (Typeable, Show)
> >
> > type Attrs =3D [Dynamic]
> >
> > attrs =3D [toDyn Masc, toDyn Second]
> >
> > gattr :: (Typeable a) =3D> Attrs -> Maybe a                  =20
> > gattr []     =3D Nothing
> > gattr (x:xs) =3D case fromDynamic x of
> >                  Nothing -> gattr xs
> >                  Just x  -> Just x
> >
> > type GetAttr a =3D Attrs -> Maybe a
> > ggender =3D gattr :: GetAttr Gender
> > gnumber =3D gattr :: GetAttr Number
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> which already is much more readable. But I'm sure
> problems are just around the corner ...
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> Thank you.
> Markus
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