答复: [Haskell-cafe] How to do this in FP way?

[Don Stewart]

dons:
> magicloud.magiclouds:
> > OK. Here it is.
> > I want to make a monitor tool for linux. It runs for a long time, and give
> > out a certain process's io stat per second. The way I get io stat is to read
> > from /proc/pid/io. But the data in this file is a total, I need to read it
> > first, then next second, read it again, and shows the difference, and go on.
> > So, what is your idea?
> 
> Easy,
> 
>     import Control.Concurrent
>     import Control.Monad
> 
>     main = go 0
>         where
>             go st = forever $ do
>                        n <- read `fmap` readFile "/proc/pid/io"
>                        print (n - st) -- display difference
>                        threadDelay (10^6)

Oops, not 'forever' :)

              go st = do
                    ...
                    go n