I would recommend that you split out your `Done` termination check into
its own isolated pipe:
untilDone :: Monad m => Pipe (Either String ScoreBoard) (Either
String ScoreBoard) m ()
untilDone = do
x <- await
yield x
case x of
Right (Done s) -> return ()
_ -> untilDone
Once you separate that out, you can greatly simplify `pipeScore` like this:
pipeScore :: (Monad m) => Board -> Pipe (Either String Int) (Either
String ScoreBoard) m ()
pipeScore = evalStateT $ for untilDone $ \x -> case x of
Left s -> lift $ yield (Left s)
Right n -> do
let y = score n b
lift $ yield y
case y of
Right (Current (_, b')) -> put b'
_ -> return ()
On 5/12/14, 8:19 AM, Pierre R wrote:
I have just updated the code (on my repo that contains MVC.hs) so that
the end of game is now considered a Right value.
So I have introduced the type:
data ScoreBoard = Done Int | Current (Int, Board) deriving (Show, Eq)
and `score` has now this signature:
score :: Int -> Board -> Either String ScoreBoard
These changes have cleaned up the MVC code a bit (for instance it does
not need to know about `isGameOver` anymore)
`pipeScore` is even more stupid than before so there must be a better
way to re-conciliate the APIs.
pipeScore :: (Monad m) => Board -> Pipe (Either String Int) (Either
String ScoreBoard) m ()
pipeScore = go
where
go b = do
for cat $ \x -> case x of
Left s -> yield (Left s)
Right n -> do
case score n b of
Right c@(Current (_, b')) -> do
yield (Right c)
go b'
Right (Done s) ->
yield $ Right (Done s)
Left msg -> do
yield (Left msg)
go b
@Patrick, my repos contain the merged code:
https://github.com/PierreR/afgame/tree/master/haskell
I will probably follow your advice about keeping only one level of
loop. I still don't get how to apply `right` from pipe-extra though
(your pipeScore' doesn't compile). I will give it another try as soon
as I understand this better. Thanks for your help.
Cheers
On Sunday, May 11, 2014 2:39:50 PM UTC+2, Davorak wrote:
@Tony - I am getting a 404 for that link[1]. The base repo is
there by I can not find the MVC example with a github search.
[1]https://github.com/tonyday567/afgame/blob/mvc-example/haskell/src/Afgame/MVC.hs
<https://github.com/tonyday567/afgame/blob/mvc-example/haskell/src/Afgame/MVC.hs>
On Wed, May 7, 2014 at 10:51 PM, Tony Day <[email protected]
<javascript:>> wrote:
Hi Pierre,
I coded up your front-end in the spirit of Gabe's mvc
library. I know you didn't ask that, of course, but G has
asked for examples of using the mvc library and your example
was perfect for the task.
https://github.com/tonyday567/afgame/blob/mvc-example/haskell/src/Afgame/MVC.hs
<https://github.com/tonyday567/afgame/blob/mvc-example/haskell/src/Afgame/MVC.hs>
I liked how it turned out. Most of the IO in the existing
pipes became messages that get wrapped as part of an Either
String (Int,Board). Not perfect but, with the pipeline
getting a bit messier.
Most fun was using quickcheck on the game logic. I can guess
from qc that the game lasts for 15 moves, that a high score is
around 200, and that moves of 15 and consecutive moves that
add up to 15 are strong. Not bad considering I haven't even
read the rules!
On Tuesday, May 6, 2014 5:32:37 AM UTC+10, Pierre R wrote:
Hi,
I have added a little pipes frontend to one of my pet
example and I was wondering how idiomatic (or not) it is.
http://lpaste.net/103623
Basically instead of consuming a list with mapM (the
`scores` function) I am streaming input from stdin.
Consequently I need to treat the end of game differently
than a bogus shot.
Nothing to do with Pipes but I am not sure annotation 2 is
better because it forces all client `score` code to unwrap
StateT whereas I only need the state monad when I have to
deal with a list of shots. Is there a more idiomatic way
to do this ?
The github repo is here :
https://github.com/PierreR/afgame/tree/master/haskell
<https://github.com/PierreR/afgame/tree/master/haskell>
Thanks for your feedback
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