[nemetroid]

It's some time since I last worked in Haskell (and I never worked on anything useful), but I would write the function this way:

  getSocketAPIPort :: Int -> IO Int
  getSocketAPIPort defaultPort = do
    maybeEnvPort <- lookupEnv "socketPort"
    return $ case maybeEnvPort of
      Nothing   -> defaultPort
      Just port -> fromMaybe defaultPort (readMaybe port)

[zeendo]

100% this is how I'd write it (except probably with pure instead of return). I don't get the desire to sprinkle bind throughout the other replies in this thread. I feel like it makes things less clear.