Benjamin,
I have managed to reduce it all to this for which I thank you, it feels much neater now...

doOption dev (Forward n)  = do
  putStrLn $ "> STEP FORWARD " ++ (show n)
  forM_ [3..0] (\b -> stepBit dev ioPORTA b)

doOption dev (Backward n) = do
  putStrLn $ "> STEP BACKWARD " ++ (show n)
  forM_ [0..3] (\b -> stepBit dev ioPORTA b)

stepBit :: HWHandle -> Word8 -> Word8 -> IO ()
stepBit dev p b = setBit p b 0 >> setBit p b 1
    where
      setBit p b s = HW.setPortBit dev p b s >> stepDelay


I think I will also try to use "forEach_" as well which means I can then compose is something that passes in [0..3] or [3..0] to the composition... I may even learn something in the process!
God I love the way that Haskell makes you *want* to reduce things to their most succint form, even if it hurts along the way.
Only Lisp ever (ha, still does!) made me feel like Haskell does, aka a total n00b after 28 years in the business! LMAO

Thanks list.



On 29 April 2013 15:07, Benjamin Edwards <edwards.benj@gmail.com> wrote:

forM_ [0..3] \b -> stepBit b .... ?

On 29 Apr 2013 15:01, "emacstheviking" <objitsu@gmail.com> wrote:
I have built a library for using the Hexwax expandIO-USB chip and I have now got some code to drive a stepper motor:

doOption :: HWHandle -> Flag -> IO ()
doOption dev (Backward n) = do
  putStrLn $ "> STEP BACKWARD " ++ (show n)
  let x = [ stepBit b | b <- [3..0]]
  return ()
    where
      stepBit p b = setBit p b 0 >> setBit p b 1
        where setBit p b s = HW.setPortBit dev p b s >> stepDelay


It feels a little smelly... if I don't assign the result of the list comprehension to "x" the return type blows at me hence the return(), to get past the door steward type checker... so what would be the "ideal" way to just execute my LC to step the bits and then return.

I thought of using "liftIO" but I think that would be "backwards" here if you catch my drift. I am already in the IO monad as it is, so that has confused me because liftIO lifts something "into" the IO monad and I am already there... this project is making me work harder at my Haskell and I think that once I've completed it I will be much further advanced with it...

So, if anybody cares to suggest more elegant and Haskell like ways to re-factor the above code I am more than happy to know about it!

All the best,
Sean.



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