Hi, folks.
I've got a working class and instances thereof. I would now like to change
the class such that error behaviour is specified by MonadError, for the
moment throwing String errors. When I try to add MonadError into the types I
eventually hit the requirement for allow-undecidable-instances.
Is there some way I can I avoid having to use this extension?
My starting point consists of:
class (Num i, Bounded i, Monad m) => MonadSource i m | m -> i where
...
newtype SourceT i m a = SourceT (StateT (Store i) m a)
deriving (Functor, Monad, MonadIO, MonadTrans)
instance (Num i, Bounded i, Monad m) => MonadSource i (SourceT i m) where
...
I changed it to:
class (Num i, Bounded i, Monad m, MonadError String m)
=> MonadSource i m | m -> i where
....
newtype SourceT i m a = SourceT (StateT (Store i) m a)
deriving (Functor, Monad, MonadIO, MonadTrans, MonadError e)
instance (Num i, Bounded i, Monad m, MonadError String m)
=> MonadSource i (SourceT i m) where
...
Thanks
Daniel
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