[Haskell-cafe] Do I Need To Write An Instance for Assertable Here?

[Ryan Ingram]

Here's the important info:
    liftMoment :: MonadMoment m => Moment a -> m a
    instance MonadMoment MomentIO
    instance MonadMoment Moment

So liftMoment gives you a MomentIO or a Moment, not an IO.  You need to do
something with that.

From
https://hackage.haskell.org/package/reactive-banana-1.0.0.0/docs/Reactive-Banana-Frameworks.html#v:compile
    compile :: MomentIO () -> IO EventNetwork

It looks like the intended usage is to compile into an EventNetwork, then
use the functions that operate on EventNetwork (like "actuate" to start
it).  If you need to get a boolean value out, you need another way to do so
(such as using reactimate to call a callback)

  -- ryan

On Fri, Nov 13, 2015 at 8:48 AM, Michael Litchard <michael at schmong.org>
wrote:

>  I think I'm on the right track. I have commented out all test harness
> code and have changed the signature for bufferPopulated
>
> bufferPopulated :: UAC -> IO Bool
> bufferPopulated ev = do
>   let eInput = ev <$ never
>       eValidated = toVAC <$> eInput
>   bBufferMap <- liftMoment ((buffer eValidated eClear) :: Moment    (Behavior BufferMap))
>   let r2 = [(Just $ BufferMap $ M.insert (AID (Data.Text.pack "100")) (toVAC ev) (M.empty :: M.Map AID VAC))]
>   r1 <- (interpret (eBuffer bBufferMap) []) :: IO [Maybe BufferMap])
>   return $ r1 == r2
>
> I believe this should work, but here's the error
>
> tests/Spec.hs:35:17:
>     No instance for (MonadMoment IO) arising from a use of ‘liftMoment’
>     In a stmt of a 'do' block:
>       bBufferMap <- liftMoment
>                       ((buffer eValidated eClear) :: Moment (Behavior   BufferMap))
>
> Let's take a look at MonadMoment from Reactive.Banana.Combinators
> class Monad m => MonadMoment m where
>  An instance of the MonadMoment class denotes a computation that happens
> at one particular moment in time.
>  Unlike the Moment monad, it need not be pure anymore.
>  Methods
>    liftMoment :: Moment a -> m a
>  Instances
>  MonadMoment MomentIO
>  MonadMoment Moment
>
> m can be any Monad, IO is a Monad. so liftMoment should lift the Moment
> Behavior (BufferMap) to IO Behavior (BufferMap) , why doesn't it. What's
> wrong with my reasoning?
>
>
> On Fri, Nov 13, 2015 at 7:16 AM, Michael Litchard <michael at schmong.org>
> wrote:
>
>> Below is some test code I am writing for my game, the link to the entire codebase, the error message and some discussion
>>
>> main :: IO ()
>> main = defaultMain
>>   [ testGroup "EventNetwork Input"
>>     [testBuffer "bBuffer" Populated]
>>   ]
>>
>> testBuffer :: String -> BufferState -> Test
>> testBuffer name Populated =
>>   testCase name $ assert $ bufferPopulated (UAC (PlayerCommand (Move (ToPlanetName Mongo)) (AID (Data.Text.pack "100"))))
>> testBuffer name Empty =
>>   testCase name $ assert $ bufferEmptied (UAC (PlayerCommand (Move (ToPlanetName Mongo)) (AID (Data.Text.pack "100"))))
>>
>> bufferPopulated :: UAC -> MomentIO Bool
>> bufferPopulated ev = do
>>   let eInput = ev <$ never
>>       eValidated = toVAC <$> eInput
>>   bBufferMap <- (buffer eValidated eClear) :: MomentIO (Behavior BufferMap)
>>   let r2 = [(Just $ BufferMap $ M.insert (AID (Data.Text.pack "100")) (toVAC ev) (M.empty :: M.Map AID VAC))]
>>   r1 <- liftIO $ ((interpret (eBuffer bBufferMap) []) :: IO [Maybe BufferMap])
>>   return $ r1 == r2
>>
>> bufferEmptied :: UAC -> MomentIO Bool
>> bufferEmptied ev = undefined
>>
>> eBuffer :: Behavior BufferMap -> Event a -> Event BufferMap
>> eBuffer bBufferMap nvr =
>>   bBufferMap <@ (() <$ nvr)
>>
>> eClear = Clear <$ (() <$ never)
>>
>>
>> When I run stack build I get
>>
>> tests/Spec.hs:26:19:
>>     No instance for (Test.HUnit.Base.Assertable (MomentIO Bool))
>>       arising from a use of ‘assert’
>> In the expression: assert
>> In the second argument of ‘($)’, namely
>>   ‘assert
>>    $ bufferPopulated
>>        (UAC
>>           (PlayerCommand (Move (ToPlanetName Mongo)) (AID (pack "100"))))’
>> In the expression:
>>   testCase name
>>   $ assert
>>     $ bufferPopulated
>>         (UAC
>>            (PlayerCommand (Move (ToPlanetName Mongo)) (AID (pack "100"))))
>>
>> The problem lies with buffer. It relies on accumB which requires the MomentIO monad. I considered writing an
>> instance for Assertable, but I think that's a red-herring and the answer lies elsewhere. I need to reconcile the
>> fact that assert wants an IO Bool, but accumB wants a MomentIO. Maybe I do need to write an instance for Assertable.
>>
>> Here's the link to the project:https://github.com/mlitchard/emporos/tree/banana-1.0.0/src
>>
>>
>
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