Réf. : [Haskell-cafe] Re: circular imports

2010-09-07 Thread corentin . dupont 
That sort of code (stripped out):

In Game.hs:

data Game = Game { ...
   activeRules :: [Rule]}

applyTo :: Rule - Game - Game
applyTo r gs = ...


In Rule.hs:

data Rule = Cond (Obs) Rule Rule
  | many others..
  deriving (Read, Show, Eq, Typeable)

data NamedRule = NamedRule { ...,
 rule :: Rule }

isRuleLegal :: Rule - NamedRule - Game - Bool
isRuleLegal = ...


In Obs.hs:

data Obs a where
 ProposedBy :: Obs Int   -- The player that proposed the tested rule
 ...


evalObs :: Obs - NamedRule - Game - EvalObsType
evalObs = ...


Corentin




   
 Johannes  
 Waldmann  
 waldm...@imn.ht Pour
 wk-leipzig.dehaskell-cafe@haskell.org
 Envoyé par :   cc
 haskell-cafe-bou  
 n...@haskell.orgObjet
   [Haskell-cafe] Re: circular imports
   
 07/09/2010 14:00  
   
   
   
   




 corentin.dupont at ext.mpsa.com writes:

 I had recently a really hard time splitting up my program into parts!
 The natural, business-oriented split up drove me into a deadly circular
 dependency.

perhaps you could post your code (enough of it to understand the problem)?

J.W.


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Re: Réf. : [Haskell-cafe] Re: circular imports

2010-09-07 Thread Henning Thielemann 
corentin.dup...@ext.mpsa.com schrieb:
 That sort of code (stripped out):
 
 In Game.hs:
 
 data Game = Game { ...
activeRules :: [Rule]}
 
 applyTo :: Rule - Game - Game
 applyTo r gs = ...
 
 
 In Rule.hs:
 
 data Rule = Cond (Obs) Rule Rule
   | many others..
   deriving (Read, Show, Eq, Typeable)
 
 data NamedRule = NamedRule { ...,
  rule :: Rule }
 
 isRuleLegal :: Rule - NamedRule - Game - Bool
 isRuleLegal = ...
 
 
 In Obs.hs:
 
 data Obs a where
  ProposedBy :: Obs Int   -- The player that proposed the tested rule
  ...
 
 
 evalObs :: Obs - NamedRule - Game - EvalObsType
 evalObs = ...

As I see there is no cycle in the types. How about defining Game, Rule,
Obs in private modules, like Private.Game, Private.Rule, Private.Obs,
and implementing the functions in public modules like Game, Rule, Obs ?

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Re: Réf. : [Haskell-cafe] Re: circular imports

2010-09-07 Thread Claus Reinke 

That sort of code (stripped out):

In Game.hs:

data Game = Game { ...
  activeRules :: [Rule]}

applyTo :: Rule - Game - Game
applyTo r gs = ...


Often, it helps to parameterize the types/functions (instead
of using recursive  modules to hardcode the parameters).

Would something like this work for your case (taking the
Game module out of the loop)?

data Game rule = Game { ...
 activeRules :: [rule]}

applyTo :: rule - Game rule - Game rule
applyTo r gs = ...


In Rule.hs:
.. 
isRuleLegal :: Rule - NamedRule - Game Rule - Bool

isRuleLegal = ...

In Obs.hs:

evalObs :: Obs - NamedRule - Game Rule - EvalObsType
evalObs = ...


For the record, I'd like to have recursive modules without
having to go outside the language (some standardized
notion of Haskell module interfaces would be nicer than
implementation-specific boot files). 


But I'd like to have parameterized modules even more,
as that would allow me to avoid many use cases of
recursive modules (again, that would seem to require
module interfaces).

Claus

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