make one wait:\index{delay a concurrent thread}
\index{wait for a file descriptor}
\begin{verbatim}
-threadDelay :: Int -> IO () -- delay rescheduling for N microseconds
-threadWait :: Int -> IO () -- wait for input on specified file descriptor
+threadDelay :: Int -> IO () -- delay rescheduling for N microseconds
+threadWaitRead :: Int -> IO () -- wait for input on specified file descriptor
+threadWaitWrite :: Int -> IO () -- (read and write, respectively).
\end{verbatim}
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