008/104: sleep

src/sleep.hs

@@ -0,0 +1,23 @@
+{-# LANGUAGE NoImplicitPrelude #-}
+
+import Prelude            (Int, IO, Maybe (Just, Nothing), String,
+                           (.), (*), (++),
+                           compare, flip, mapM_, putStrLn)
+import Control.Concurrent (threadDelay)
+import Control.Monad      ((>>=), (>>))
+import Data.List          (sortBy)
+import System.Environment (getArgs)
+import System.Exit        (exitFailure)
+import Text.Read          (readMaybe)
+
+microseconds :: Int
+microseconds = 1000000
+
+sleep :: String -> IO ()
+sleep time = wait (readMaybe time)
+    where wait Nothing  = putStrLn ("sleep: invalid time interval ‘" ++ time ++ "’") >> exitFailure
+          wait (Just n) = threadDelay (n * microseconds)
+
+main :: IO ()
+main = getArgs >>= mapM_ sleep . sortBy (flip compare) -- sort args to handle non-integer values firstly
+