Putting a constraint on the MonadIO class actually makes your code
less general rather than more since it prevents your code from ever
being used in a purely functional setting. If you leave out this
constraint, you can actually turn your code into a pure function by
doing things like feed
> class StreamMonad m where
> fetchLine = m
> sendLine = String -> m ()
>
> instance StreamMonad IO where
> fetchLine = getLine
> sendLine = putLine
>
> fetchLineFromStream = lift fetchLine
> sendLineToStream = lift . sendLine
This approach makes more sense to me. The
Oh, and I just thought of one more approach:
class StreamMonad m where
fetchLine = m
sendLine = String -> m ()
instance StreamMonad IO where
fetchLine = getLine
sendLine = putLine
fetchLineFromStream = lift fetchLine
sendLineToStream = lift . sendLine
type PDSta
It isn't clear what it is that you are trying to generalize the code
to do. If you are trying to generalize it to work with an arbitrary
input/output stream of lines, then unless you are doing arbitrary I/O
it seems to me that all of these instance declarations are overkill.
All that you
On Mon, Oct 5, 2009 at 11:54 PM, Floptical Logic
wrote:
>> Instead of specifying the monad implementation, specify the interface.
>> That is, you are using state operations (from MonadState) and IO
>> operations (from MonadIO). Try removing all the type signatures that
>> mention PDState and see w
On Mon, Oct 5, 2009 at 10:54 PM, Floptical Logic
wrote:
>
> If I were to make an instance of MonadIO be a parameter to StateT and
> I wanted to use the Net monad (from Roll your own IRC bot on the wiki)
> with it, I would need to make Net an instance of MonadIO. What would
> this instance look li
> Instead of specifying the monad implementation, specify the interface.
> That is, you are using state operations (from MonadState) and IO
> operations (from MonadIO). Try removing all the type signatures that
> mention PDState and see what you get.
>
> E.g., loop :: (MonadState PD m, MonadIO m) =
My thought is that you could simply drop the IO from your type
definition,
type PDState = StateT PD
You will need to change all of your type signature from "PDState
" to "PDState m " to make them all polymorphic over the
choice of monad. Then all you should need to do is to generalize the
On Mon, Oct 5, 2009 at 7:56 PM, Floptical Logic wrote:
> The code below is a little interactive program that uses some state.
> It uses StateT with IO to keep state. My question is: what is the
> best way to generalize this program to work with any IO-like
> monad/medium? For example, I would li
The code below is a little interactive program that uses some state.
It uses StateT with IO to keep state. My question is: what is the
best way to generalize this program to work with any IO-like
monad/medium? For example, I would like the program to function as it
does now using stdin but I woul
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