getCategoriesInCriterion :: ChordProgressionDatabase -> String -> [String]
--getCategoriesInCriterion (ChordProgressionDatabase list) criterion = Data.Map.mapMaybe ((flip Data.Map.lookup) criterion $ fst) list
getCategoriesInCriterion (ChordProgressionDatabase list) criterion = nub $ Data.Maybe.mapMaybe (\ cpMap -> Data.Map.lookup criterion cpMap) (map fst list)
getCategoriesInCriterion :: ChordProgressionDatabase -> String -> [String]
getCategoriesInCriterion (ChordProgressionDatabase list) criterion = nub $ Data.Maybe.mapMaybe (\ cpMap -> Data.Map.lookup criterion cpMap) (map fst list)
getCategoriesInCriterion (ChordProgressionDatabase list) criterion = nub $ Data.Maybe.mapMaybe (\ cpMap -> Data.Map.lookup criterion cpMap) (map fst list)