Re: [Haskell-beginners] cyclic dependency problem

El Mar 5, 2015, a las 8:43, Konstantin Saveljev escribió:

Hello,

I'm having some trouble with cyclic dependency.

My simplified version of hierarchy:

module A where

import MyState

data A a = A (StateT MyState IO a) deriving (...)

Now there is a module MyState:

module MyState where

import SomeType

data MyState = MyState { st :: SomeType, ... }

Finally the module that introduces cyclic dependency:

module SomeType where

import A

data SomeType = SomeType { f :: A (), ... }

I have been suggested to move the types into one module and then import it wherever needed. But the problem is that even if I put them into one file those three data types still form a cyclic dependency and compiler throws errors saying "i don't know about this"

So if I have a single module:

data A a = A (StateT MyState IO a) deriving (...) data MyState = MyState { st :: SomeType, ... } data SomeType = SomeType { f :: A (), ... }

With this setup the compiler is gonna tell us it doesn't know about MyState. And no matter how we shuffle these types within a file we are still getting some "unknowns"

Did you try it? It should work fine -- haskell doesn't care about the order of data declarations within a file. Tom

How would one approach such a problem?

Best regards, Konstantin _______________________________________________ Beginners mailing list Beginners@haskell.org http://mail.haskell.org/cgi-bin/mailman/listinfo/beginners