>>> parseSeed "--seed=6" Just 6 >>> parseSeed "--seeeed=6" Nothing
>>> parseThreads "-j6" Just 6 >>> parseThreads "-j-2" Nothing >>> parseThreads "-jA" Nothing
> outernmostPrec "1 + 2" Just 6
>>> die "Goodbye!" Goodbye! *** Exception: ExitFailure 1
runThrow (throwError e >>= k) = runThrow (throwError e)