Re: [Haskell-cafe] Stacking data types

On 06/04/11 20:32, Brandon Moore wrote:

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From: Yves Parès 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.

_______________________________________________ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe I was struggling with this idea a few weeks ago. I think I tried the same types of extensions that you have, also with no luck.

I then started looking at extensible records on the Haskell wiki http://www.haskell.org/haskellwiki/Extensible_record This was the one I liked, but as far as I could tell it has not been implemented (please tell me if I was wrong about that) http://research.microsoft.com/en-us/um/people/simonpj/Haskell/records.html RS