I've got some code which could be made simpler, I hope. the problem is this: I am implementing a software sampling synthesizer. For a given musical instrument, like piano, there are sound samples in memory. One purchases or creates sample sets. To save time money & resources, most sample sets are not complete---they have samples for only some of the pitches. Perhaps every third pitch has a sample. For the software to produce the sound for a non-included pitch, the software finds the closest included sample and plays it back slightly slower/faster to get the target pitch. That leads to the following code. Any ideas for improvement are welcome. The problem is that there are many cases to check: an empty map? the requested pitch less than all available pitches, greater than all available, or somewhere between? I am specifically writing this to run in O( log n) time. (It would be simpler as O(n).) This particular algorithm probably doesn't need to run in O(log n) time, but I want to do it as an educational experience---I will have other applications that need to use Map in O(log n) time. import Control.Monad.Identity import Control.Monad.Error import Control.Monad import qualified Data.Map as M type Pitch = Int type Sample = String type SampleMap = M.Map Pitch Sample -- Given a SampleMap and a Pitch, find the Pitch in the SampleMap -- which is closest to the supplied Pitch and return that. Also -- handle case of null map by throwing an error. findClosestPitch :: SampleMap -> Pitch -> ErrorT String Identity Pitch findClosestPitch samples inPitch = do when (M.null samples) $ throwError "Was given empty sample table." case M.splitLookup inPitch samples of (_,Just _,_ ) -> return inPitch (m1,_ ,m2) | (M.null m1) && not (M.null m2) -> case1 | not (M.null m1) && (M.null m2) -> case2 | otherwise -> case3 where case1 = return . fst . M.findMin $ m2 case2 = return . fst . M.findMax $ m1 case3 = return $ closest (fst . M.findMax $ m1) (fst . M.findMin $ m2) closest a b = if abs (a - inPitch) < abs (b - inPitch) then a else b