<div dir="ltr">Guys, I'm so sorry. It actually turned out to be the problem with makeLenses (from Control.Lens) which I also put into the same module. Now that this stuff is in separate modules everything works and deriving is not a problem. I'm so sorry for wasting you time and thank you very much for your help.<div><br></div><div>Konstantin</div></div><div class="gmail_extra"><br><div class="gmail_quote">On Thu, Mar 5, 2015 at 4:50 PM, Konstantin Saveljev <span dir="ltr"><<a href="mailto:konstantin.saveljev@gmail.com" target="_blank">konstantin.saveljev@gmail.com</a>></span> wrote:<br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div dir="ltr">Would this be a correct implementation?:<div><br></div><div><div>{-# LANGUAGE MultiParamTypeClasses #-} -- for some reason compiler says to use it ?</div><div><br></div><div>import qualified Control.Monad.State.Lazy as Lazy</div><div><br></div><div>instance MonadState MyState X where</div><div> get = X Lazy.get</div><div> put s = X $ Lazy.put s</div></div><span class="HOEnZb"><font color="#888888"><div><br></div><div><br></div><div>Konstantin</div></font></span></div><div class="HOEnZb"><div class="h5"><div class="gmail_extra"><br><div class="gmail_quote">On Thu, Mar 5, 2015 at 4:37 PM, Konstantin Saveljev <span dir="ltr"><<a href="mailto:konstantin.saveljev@gmail.com" target="_blank">konstantin.saveljev@gmail.com</a>></span> wrote:<br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div dir="ltr">I believe Francesco has a point here. I do have "deriving (MonadState MyState)" which is probably causing the problem.<div><br></div><div>Unfortunately I'm not capable of writing the instance myself. Maybe someone could help me?</div><div><br></div><div>My full declaration looks something like this:</div><div><br></div><div><div> newtype X a = X (StateT MyState (ExceptT String IO) a)</div><div> deriving (Functor, Applicative, Monad, MonadIO, MonadError String, MonadState MyState)</div></div><div><br></div><div>If I was to remove "MonadState MyState" from the "deriving" section, how would one implement it?</div><span><font color="#888888"><div><br></div><div><br></div><div>Konstantin</div></font></span></div><div><div><div class="gmail_extra"><br><div class="gmail_quote">On Thu, Mar 5, 2015 at 4:25 PM, <span dir="ltr"><<a href="mailto:amindfv@gmail.com" target="_blank">amindfv@gmail.com</a>></span> wrote:<br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><br>
<br>
El Mar 5, 2015, a las 8:43, Konstantin Saveljev <<a href="mailto:konstantin.saveljev@gmail.com" target="_blank">konstantin.saveljev@gmail.com</a>> escribió:<br>
<div><div><br>
> Hello,<br>
><br>
> I'm having some trouble with cyclic dependency.<br>
><br>
> My simplified version of hierarchy:<br>
><br>
> module A where<br>
><br>
> import MyState<br>
><br>
> data A a = A (StateT MyState IO a) deriving (...)<br>
><br>
> Now there is a module MyState:<br>
><br>
> module MyState where<br>
><br>
> import SomeType<br>
><br>
> data MyState = MyState { st :: SomeType, ... }<br>
><br>
> Finally the module that introduces cyclic dependency:<br>
><br>
> module SomeType where<br>
><br>
> import A<br>
><br>
> data SomeType = SomeType { f :: A (), ... }<br>
><br>
> 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"<br>
><br>
> So if I have a single module:<br>
><br>
> data A a = A (StateT MyState IO a) deriving (...)<br>
> data MyState = MyState { st :: SomeType, ... }<br>
> data SomeType = SomeType { f :: A (), ... }<br>
><br>
> 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"<br>
><br>
<br>
</div></div>Did you try it? It should work fine -- haskell doesn't care about the order of data declarations within a file.<br>
<br>
Tom<br>
<span><br>
<br>
> How would one approach such a problem?<br>
><br>
> Best regards,<br>
> Konstantin<br>
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