[Haskell-beginners] until and Time

[Steve Klabnik]

Hello everyone. I have a quick question about Time.

I was talking about Haskell on the Arch Linux forums today, and someone was
trying to put together code that would print a series of periods for, say, 5
minutes. I felt like using 'until' would be the most correct way of going
about it, but when I tried to do it...


import Time

makeLater      :: ClockTime -> ClockTime
makeLater t    =  addToClockTime (TimeDiff 0 0 0 0 0 5 0) t

updateTime :: ClockTime -> ClockTime
updateTime t = t

main = do
  start <- getClockTime
  until ((==) $ makeLater start) (updateTime) start
  putStrLn "done"

Now, updateTime isn't correct. And this wouldn't print any periods. But GHC
is giving me errors:

$ runhaskell temp.hs

temp.hs:11:2:
    Couldn't match expected type `IO t'
           against inferred type `ClockTime'
    In the expression:
        until ((==) $ makeLater start) (updateTime) start
    In a 'do' expression:
        until ((==) $ makeLater start) (updateTime) start
    In the expression:
        do start <- getClockTime
           until ((==) $ makeLater start) (updateTime) start
           putStrLn "done"

I'm not sure where IO t is coming from at all. Am I even on the right track?
How would you write this code?
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