Re: [Haskell-cafe] [C][enums][newbie] What is natural Haskell representation of such enum?

2012-01-23 Thread Malcolm Wallace 

 2012/1/22 Данило Глинський abcz2.upr...@gmail.com
 What is natural Haskell representation of such enum?
 
 enum TypeMask
 {
UNIT,
GAMEOBJECT,
 
CREATURE_OR_GAMEOBJECT = UNIT | GAMEOBJECT
 };

I don't think that definition makes any sense in C, because UNIT is 0, so UNIT 
| GAMEOBJECT == GAMEOBJECT == 1

Nevertheless, in Haskell something vaguely similar might be:

data TypeMask = UNIT | GAMEOBJECT | CREATURE_OR_GAMEOBJECT

 // 1-byte flaged enum
 enum TypeMask
 {
// ...
UNIT= 0x0004,
GAMEOBJECT  = 0x0008,
// ...
 
CREATURE_OR_GAMEOBJECT = UNIT | GAMEOBJECT
WORLDOBJECT = UNIT | PLAYER | GAMEOBJECT | DYNAMICOBJECT | CORPSE 
// ... even more enum combos ...
 };

import Data.Bits
data TypeMask = UNIT | GAMEOBJECT | CREATURE_OR_GAMEOBJECT | WORLDOBJECT
instance Enum TypeMask where
fromEnum UNIT = 0x4
fromEnum GAMEOBJECT = 0x8
fromEnum CREATURE_OR_GAMEOBJECT = fromEnum UNIT .|. fromEnum GAMEOBJECT
fromEnum WORLDOBJECT = fromEnum UNIT .|. fromEnum PLAYER .|. fromEnum 
GAMEOBJECT
   .|. fromEnum DYNAMICOBJECT .|. fromEnum CORPSE

toEnum 0x4 = UNIT
toEnum 0x8 = GAMEOBJECT
toEnum _   = error unspecified enumeration value of type TypeMask

isCreatureOrGameObject :: Int - Bool
isCreatureOrGameObject x = (x .|. fromEnum CREATURE_OR_GAMEOBJECT) /= 0

isWorldObject :: Int - Bool
isWorldObject x = (x .|. fromEnum WORLDOBJECT) /= 0

-- But fundamentally, this is not an idiomatic Haskell way of doing things.
-- The other posts in this thread have shown more Haskell-ish translations.



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Re: [Haskell-cafe] [C][enums][newbie] What is natural Haskell representation of such enum?

2012-01-23 Thread Daniel Hlynskyi 
Thanks. This and previous email are answers to question I asked. But not
the answer to question I mean.
I'll describe the whole task, as Yves Parès suggested.

I'm trying to convert C++ code to Haskell. I have such hierarchy: class
Object, class Item : Object, class Container : Item. Another one example:
class Unit : Object, class Player : Unit. Each constructor do things like
this:

Object::Object()
{
objectType= TYPEMASK_OBJECT;
// ... lots of code ...
}


Item::Item()
{
objectType |= TYPEMASK_ITEM;
// ...
}

Container::Container(): Item()
{
objectType |= (TYPEMASK_ITEM | TYPEMASK_CONTAINER);
// ...
}


What is objectType? This field is used when a networksend packet is
created. In the packet it is 1 byte of flags, so it is in object hierarchy.

So the question was: what type should objectType field have in Haskell? I
think it must not mimic enum. What the structure have I to use? There is
one more problem - there may be lots of objects, lots of, so memory
efficiency is also suggested.
And side question: what to do with classes? =) Maybe there is simple rule
to convert OO hierarchy to FP.

23 січня 2012 р. 12:15 Malcolm Wallace malcolm.wall...@me.com написав:


  2012/1/22 Данило Глинський abcz2.upr...@gmail.com
  What is natural Haskell representation of such enum?
 
  enum TypeMask
  {
 UNIT,
 GAMEOBJECT,
 
 CREATURE_OR_GAMEOBJECT = UNIT | GAMEOBJECT
  };

 I don't think that definition makes any sense in C, because UNIT is 0, so
 UNIT | GAMEOBJECT == GAMEOBJECT == 1

 Nevertheless, in Haskell something vaguely similar might be:

 data TypeMask = UNIT | GAMEOBJECT | CREATURE_OR_GAMEOBJECT

  // 1-byte flaged enum
  enum TypeMask
  {
 // ...
 UNIT= 0x0004,
 GAMEOBJECT  = 0x0008,
 // ...
 
 CREATURE_OR_GAMEOBJECT = UNIT | GAMEOBJECT
 WORLDOBJECT = UNIT | PLAYER | GAMEOBJECT | DYNAMICOBJECT | CORPSE
 // ... even more enum combos ...
  };

 import Data.Bits
 data TypeMask = UNIT | GAMEOBJECT | CREATURE_OR_GAMEOBJECT | WORLDOBJECT
 instance Enum TypeMask where
fromEnum UNIT = 0x4
fromEnum GAMEOBJECT = 0x8
fromEnum CREATURE_OR_GAMEOBJECT = fromEnum UNIT .|. fromEnum GAMEOBJECT
fromEnum WORLDOBJECT = fromEnum UNIT .|. fromEnum PLAYER .|. fromEnum
 GAMEOBJECT
   .|. fromEnum DYNAMICOBJECT .|. fromEnum CORPSE

toEnum 0x4 = UNIT
toEnum 0x8 = GAMEOBJECT
toEnum _   = error unspecified enumeration value of type TypeMask

 isCreatureOrGameObject :: Int - Bool
 isCreatureOrGameObject x = (x .|. fromEnum CREATURE_OR_GAMEOBJECT) /= 0

 isWorldObject :: Int - Bool
 isWorldObject x = (x .|. fromEnum WORLDOBJECT) /= 0

 -- But fundamentally, this is not an idiomatic Haskell way of doing things.
 -- The other posts in this thread have shown more Haskell-ish translations.



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Re: [Haskell-cafe] [C][enums][newbie] What is natural Haskell representation of such enum?

2012-01-23 Thread David Barbour 
If you want a simple translation, use Word8 (from Data.Word) for the type
and use Data.Bits for operations on it just like in C++. This would offer
you storage efficiency (if stored as a strict field).

If you want idiomatic Haskell, constructor of the form:

  data ObjectType = Object | Item | Container | Unit | Player, etc.

Then simply put intelligence into the `isContainer` or `toWord8`, etc.
translations. This latter approach will be more extensible in the long run,
since you might find you want some parameterized object types.

Re: OO Classes and Haskell

If your classes are more like `interfaces`, you could use Typeclasses to
model them. Otherwise, look into OOHaskell. But I think your program
architecture will simply be different in idiomatic Haskell than in
idiomatic C++.

Regards,

Dave


On Mon, Jan 23, 2012 at 1:14 PM, Daniel Hlynskyi abcz2.upr...@gmail.comwrote:

 Thanks. This and previous email are answers to question I asked. But not
 the answer to question I mean.
 I'll describe the whole task, as Yves Parès suggested.

 I'm trying to convert C++ code to Haskell. I have such hierarchy: class
 Object, class Item : Object, class Container : Item. Another one example:
 class Unit : Object, class Player : Unit. Each constructor do things like
 this:

 Object::Object()
 {
 objectType= TYPEMASK_OBJECT;
 // ... lots of code ...
 }


 Item::Item()
 {
 objectType |= TYPEMASK_ITEM;
 // ...
 }

 Container::Container(): Item()
 {
 objectType |= (TYPEMASK_ITEM | TYPEMASK_CONTAINER);
 // ...
 }


 What is objectType? This field is used when a networksend packet is
 created. In the packet it is 1 byte of flags, so it is in object hierarchy.

 So the question was: what type should objectType field have in Haskell? I
 think it must not mimic enum. What the structure have I to use? There is
 one more problem - there may be lots of objects, lots of, so memory
 efficiency is also suggested.
 And side question: what to do with classes? =) Maybe there is simple rule
 to convert OO hierarchy to FP.

 23 січня 2012 р. 12:15 Malcolm Wallace malcolm.wall...@me.com написав:


  2012/1/22 Данило Глинський abcz2.upr...@gmail.com
  What is natural Haskell representation of such enum?
 
  enum TypeMask
  {
 UNIT,
 GAMEOBJECT,
 
 CREATURE_OR_GAMEOBJECT = UNIT | GAMEOBJECT
  };

 I don't think that definition makes any sense in C, because UNIT is 0, so
 UNIT | GAMEOBJECT == GAMEOBJECT == 1

 Nevertheless, in Haskell something vaguely similar might be:

 data TypeMask = UNIT | GAMEOBJECT | CREATURE_OR_GAMEOBJECT

  // 1-byte flaged enum
  enum TypeMask
  {
 // ...
 UNIT= 0x0004,
 GAMEOBJECT  = 0x0008,
 // ...
 
 CREATURE_OR_GAMEOBJECT = UNIT | GAMEOBJECT
 WORLDOBJECT = UNIT | PLAYER | GAMEOBJECT | DYNAMICOBJECT | CORPSE
 // ... even more enum combos ...
  };

 import Data.Bits
 data TypeMask = UNIT | GAMEOBJECT | CREATURE_OR_GAMEOBJECT | WORLDOBJECT
 instance Enum TypeMask where
fromEnum UNIT = 0x4
fromEnum GAMEOBJECT = 0x8
fromEnum CREATURE_OR_GAMEOBJECT = fromEnum UNIT .|. fromEnum GAMEOBJECT
fromEnum WORLDOBJECT = fromEnum UNIT .|. fromEnum PLAYER .|. fromEnum
 GAMEOBJECT
   .|. fromEnum DYNAMICOBJECT .|. fromEnum CORPSE

toEnum 0x4 = UNIT
toEnum 0x8 = GAMEOBJECT
toEnum _   = error unspecified enumeration value of type TypeMask

 isCreatureOrGameObject :: Int - Bool
 isCreatureOrGameObject x = (x .|. fromEnum CREATURE_OR_GAMEOBJECT) /= 0

 isWorldObject :: Int - Bool
 isWorldObject x = (x .|. fromEnum WORLDOBJECT) /= 0

 -- But fundamentally, this is not an idiomatic Haskell way of doing
 things.
 -- The other posts in this thread have shown more Haskell-ish
 translations.




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Re: [Haskell-cafe] [C][enums][newbie] What is natural Haskell representation of such enum?

2012-01-23 Thread Mike Burns 
On 2012-01-23 13.45.50 -0800, David Barbour wrote:
 If your classes are more like `interfaces`, you could use Typeclasses to
 model them. Otherwise, look into OOHaskell. But I think your program
 architecture will simply be different in idiomatic Haskell than in
 idiomatic C++.

If your OO is very design patterned, and especially if it prefers
composition over inheritence, you can port it sorta directly, sometimes.

For example, all the classes that implement an interface become a sum
type, and their methods are functions that take a value of the sum type.

interface MusicCompilation { def trackListing() : [Song] }
class Record implements MusicCompilation { ... }
class BlogPost implements MusicCompilation { ... }

Could translate to

data MusicCompilation = Record [Song] | BlogPost [Song]

trackListing (Record xs) = xs
trackListing (BlogPost xs) = xs

The more your OO looks like C, the harder this will be.

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[Haskell-cafe] [C][enums][newbie] What is natural Haskell representation of such enum?

2012-01-22 Thread Данило Глинський 
What is natural Haskell representation of such enum?

enum TypeMask
{
   UNIT,
   GAMEOBJECT,

   CREATURE_OR_GAMEOBJECT = UNIT | GAMEOBJECT
};

More sophisticated question is: and what data structures must be used when
converting this naturally one to Haskell?

// 1-byte flaged enum
enum TypeMask
{
   // ...
   UNIT= 0x0004,
   GAMEOBJECT  = 0x0008,
   // ...

   CREATURE_OR_GAMEOBJECT = UNIT | GAMEOBJECT
WORLDOBJECT = UNIT | PLAYER | GAMEOBJECT | DYNAMICOBJECT | CORPSE
   // ... even more enum combos ...
};
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Re: [Haskell-cafe] [C][enums][newbie] What is natural Haskell representation of such enum?

2012-01-22 Thread David Barbour 
Performing bit-mask operations is possible via the Data.Bits operations (on
elements of type Word8 or Word16, etc.). But I must say, it doesn't seem
very `natural` in Haskell, nor even in other languages. It crosses lines,
binding abstraction to representation in order to improve efficiency.

The natural way in Haskell to model model `CREATURE_OR_GAMEOBJECT` would
simply be as a function (e.g. of type Object - Bool, or ObjectType -
Bool).

Regards,

Dave

2012/1/22 Данило Глинський abcz2.upr...@gmail.com

 What is natural Haskell representation of such enum?

 enum TypeMask
 {
UNIT,
GAMEOBJECT,

CREATURE_OR_GAMEOBJECT = UNIT | GAMEOBJECT
 };

 More sophisticated question is: and what data structures must be used when
 converting this naturally one to Haskell?

 // 1-byte flaged enum
 enum TypeMask
 {
// ...
UNIT= 0x0004,
GAMEOBJECT  = 0x0008,
// ...

CREATURE_OR_GAMEOBJECT = UNIT | GAMEOBJECT
 WORLDOBJECT = UNIT | PLAYER | GAMEOBJECT | DYNAMICOBJECT | CORPSE
// ... even more enum combos ...
 };

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Re: [Haskell-cafe] [C][enums][newbie] What is natural Haskell representation of such enum?

2012-01-22 Thread Erik de Castro Lopo 
Данило Глинський wrote:

 What is natural Haskell representation of such enum?
 
 enum TypeMask
 {
UNIT,
GAMEOBJECT,
 
CREATURE_OR_GAMEOBJECT = UNIT | GAMEOBJECT
 };


data ObjectType = Unit | GameObject

creatureOrGameObject :: ObjectType - Bool
creatureOrGameObject Unit = True
creatureOrGameObject GameObject = True
creatureOrGameObject _ = False

 More sophisticated question is: and what data structures must be used when
 converting this naturally one to Haskell?
 
 // 1-byte flaged enum
 enum TypeMask
 {
// ...
UNIT= 0x0004,
GAMEOBJECT  = 0x0008,
// ...
 
CREATURE_OR_GAMEOBJECT = UNIT | GAMEOBJECT
 WORLDOBJECT = UNIT | PLAYER | GAMEOBJECT | DYNAMICOBJECT | CORPSE
// ... even more enum combos ...
 };

Pretty much as above, add all the different single bit masks as
constructors to ObjectType and define functions for the ones
that are a combination of one ore more constructor.

Erik
-- 
--
Erik de Castro Lopo
http://www.mega-nerd.com/

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Re: [Haskell-cafe] [C][enums][newbie] What is natural Haskell representation of such enum?

2012-01-22 Thread Yves Parès 
I may be curious to see how you intend to use such enum...
It is very C-wise, I'm not sure it will be very handy, but I need some
context.

2012/1/22 Данило Глинський abcz2.upr...@gmail.com

 What is natural Haskell representation of such enum?

 enum TypeMask
 {
UNIT,
GAMEOBJECT,

CREATURE_OR_GAMEOBJECT = UNIT | GAMEOBJECT
 };

 More sophisticated question is: and what data structures must be used when
 converting this naturally one to Haskell?

 // 1-byte flaged enum
 enum TypeMask
 {
// ...
UNIT= 0x0004,
GAMEOBJECT  = 0x0008,
// ...

CREATURE_OR_GAMEOBJECT = UNIT | GAMEOBJECT
 WORLDOBJECT = UNIT | PLAYER | GAMEOBJECT | DYNAMICOBJECT | CORPSE
// ... even more enum combos ...
 };

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