David Menendez wrote:
> 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 like the program to function as it
>> does now using stdin but I would also like it to function over IRC
>> using the Net monad from
>> <http://haskell.org/haskellwiki/Roll_your_own_IRC_bot>. Thanks for
>> any suggestions.
>
> 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) => m a
Alternatively, you can use algebraic data types instead of type classes
to generalize one program to different implementations. For monads, this
can be achieved with
http://hackage.haskell.org/package/MonadPrompt
In particular, the idea is to turn every effect like
getLine
into a constructor
GetLine
and have different implementations pattern match on that.
Regards,
apfelmus
--
http://apfelmus.nfshost.com
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