[Haskell-cafe] Stacking data types

[Brandon Moore]

>From: Yves Parès <limestrael at gmail.com>
>Sent: Wed, April 6, 2011 1:57:51 PM
>
>Hello Café,
>
>I'm trying to get some modular data types.
>The idea that came to me is that I could stack them, for instance :
>
>data Character a = Character { life :: Int,
>                               charaInner :: a }
>
>data Gun a = Gun { firepower :: Int,
>                   gunInner :: a }
>
>data Armor a = Armor { resistance :: Int,
>                       armorInner :: a }
>
>Then a character with a gun and an armor can be build this way:
>
>chara = Character 100 $ Armor 40 $ Gun 12
>
>The idea now is to be able to get some part of the character:

I don't have a better design to suggest, but I think this may end up more
complicated than you want. In particular, it will probably be complicated to
make a collection of characters that have e.g. an Armor but maybe any
other stuff.

If you do want to use this sort of design, check out Wouter Swiestra's
paper "Data Type a la Cart".

Brandon.