Patrick LeBoutillier wrote:
Michael,
Your code is interesting and I'd like to run it, but I'm not to familiar with Maps and Monad transformers. Could you provide a function to create a SampleMap and a way to test it from ghci?
Sure, 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 testMap1 = M.fromList [ (1,"sample1") , (5,"sample2") , (9,"sample3") ] -- testMap2 ==> Right 1 testMap2 = runIdentity $ runErrorT $ findClosestPitch testMap1 2 -- testMap3 ==> Right 5 testMap3 = runIdentity $ runErrorT $ findClosestPitch testMap1 5 -- testMap4 ==> Left "Was given empty sample table." testMap4 = runIdentity $ runErrorT $ findClosestPitch M.empty 5