when (any isNothing cidrs) $ do
hPutStrLn stderr "ERROR: not valid CIDR notation:"
-- Output the bad lines, safely.
let pairs = zip cidr_strings cidrs
when (any isNothing cidrs) $ do
hPutStrLn stderr "ERROR: not valid CIDR notation:"
-- Output the bad lines, safely.
let pairs = zip cidr_strings cidrs