On 06/04/11 20:32, Brandon Moore wrote:
From: Yves Parès<[email protected]>
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.
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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
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