I have a Haskell program that computes music compositions. A composition consists of sounds that happen at locations. A location is data type Loc. At each location is a list of chords. A chord is data type Chord. Each chord contains some chord-specific data and a list of notes. A note is data type Note. So we have data Note = Note ... data Chord = Chord ChordSpecificData [Note] type Composition = Map Loc [Chord] I would like to write a few different functions that operate over all the notes. The following function breaks out all the notes, tupling them with the associated Locs and Chords: compositionToList :: Composition -> [(Loc,Chord,Note)] The following function transforms Notes, keeping only the Just results. If a Chord gets all its notes eliminated, that Chord is removed. If a Loc has all its Chords removed, that Loc is removed from the Map. mapNotesMaybe :: (Loc -> Chord -> Note -> Maybe Note) -> Composition -> Composition Any advice for concise code appreciated. Dennis What's a concise way of doing this? Another useful function would be used for mapping Dennis