On Wed, Mar 4, 2009 at 3:58 PM, Conrad Meyer
On Wednesday 04 March 2009 02:45:00 pm Patrick LeBoutillier wrote:
My understanding is that what is really "passed" to the skip function is something like this:
putStrLn "2" >> putStrLn "3"
Here is my question: is it possible for the skip function to return the number of actions that were skipped? In other words, is it possible to go through the chain above without executing the actions but counting them instead?
I am also a beginner (so I am probably wrong), but I think actually the (>>) function turns two IO actions into one, and your function only recieves that one IO action. I am not sure if that can be decomposed or not (probably not).
Regards, -- Conrad Meyer
Actually, you're exactly right. The type of (>>) is (>>) :: IO a -> IO b -> IO b. Since there is no primitive IO b -> Int (which counts the number of actions in the IO action), there's no way to count them. However, there is a way to solve the original problem. If you define a list of the actions (let a = [putStrLn "2", putStrLn "3"]) then you can use length to count the number of actions in the list and sequence_ (:: [IO a] -> IO (), from Control.Monad) to run them. Alex