[platz]

i like it, for some reason my brain dislikes switching from left/right a lot, so that's why i often avoid the $ operator, so instead I'd write:

    return . fromMaybe defaultPort (maybeEnvPort >>= readMaybe)

[dllthomas]

"Have the data flow in one direction" is a good rule of thumb in writing clear Haskell code.

That said, your conversion away from $ changes the meaning here (in a way that doesn't typecheck, I think - remember that regular function application binds tightest whereas dollar binds loosest) and you still don't achieve your goal.

Instead, maybe

   return . fromMaybe defaultPort $ readMaybe =<< maybeEnvPort

or even

   return $ fromMaybe defaultPort $ readMaybe =<< maybeEnvPort

If you still don't like the dollar signs, we can parenthesize instead in two correct ways, although I don't find them more readable:

    (return . fromMaybe defaultPort) (readMaybe =<< maybeEnvPort)

    return (fromMaybe defaultPort (readMaybe =<< maybeEnvPort))