Curious problem... Suppose MyMonad is a Monad other than the IO Monad. Consider the following piece of code:
f :: MyMonad () f = action1
Now suppose also that ioToMyMonad converts an IO Monad to a MyMonad Monad:
ioToMyMonad :: IO a -> MyMonad a ioToMyMonad = return . unsafePerformIO
Suppose also that action1 needs to perform some IO operation (called IO_op), which returns IO (). In other words, action1 would be:
action1 :: MyMonad () action1 = do -- MyMonad operations ioToMyMonad $ IO_op -- other MyMonad operations
When I run f (via runMyMonad or something like that), I noticed that the io operation (IO_op) is not executed. I guess that this happens because of laziness properties, since the value returned by IO_op is useless to MyMonad. I have then two questions: 1. Does this really happen because of laziness properties? 2. Which is the best way to force IO_op to be performed? I tried the following approach: Step1: Change the type of IO_op from "IO ()" to "IO Bool" and make it returns True. Step2: Change action1 to
action1 :: MyMonad Bool action1 = do -- MyMonad operations b <- ioToMyMonad $ IO_op -- other MyMonad operations return b
Step3: Change the type of f to MyMonad Bool Step4: Finally, use this boolean somewhere after calling "runMyMonad", e. g., printing it on the screen. I'm sure this is not the best approach, so I'd really appreciate any suggestions. [I'm sending this mail to the HOpenGL list also because runMyMonad is being called inside the display callback, so perhaps it may have something to do with the problem] Thanks a lot, -- Andre