On Mon, Apr 21, 2014 at 2:55 PM, Greg Weber
agreed. additionally, while when/unless/whenM/unlessM gets rid of a `return ()` branch, ifM does not. In situations where I have branching code containing more than just properly curried functions I will prefer an intermediate variable if I get to use the language built-in if/then/else that gets syntax highlighted and avoids parentheses. `$ do` avoids parentheses with when/unless/whenM/unlessM, but with a second branch the parentheses return for both.
Looking at my own uses of 'ifM', I use it either when the branches are short: ifM ((<=) <$> Pitches.pitch_nn prev_pitch <*> Pitches.pitch_nn this_pitch) (return (Pitch.Diatonic (-1))) (return (Pitch.Diatonic 1)) ifM (Maybe.isJust <$> get) cmd_advance (cmd_set play_selected_tracks) ifM (not . wanted <$> State.get_track_title track_id) (return Nothing) (f block_id track_id events) Or when the first branch is a short exception: ifM (Directory.doesFileExist fn) (return (Just fn)) $ ifM (Directory.doesFileExist (fn ++ "c")) (return (Just (fn ++ "c"))) (return Nothing) stretch_to_1 <- ifM Internal.is_root_block (return id) $ do ) $ \omit _args deriver -> ifM (Util.chance omit) (return mempty) $ do Granted that first one is not very good.