{-# LANGUAGE NoMonomorphismRestriction #-} import Data.List import Control.Monad import Control.Applicative -- Can the function below be tweaked to quit on blank input, provisioned in the applicative style? -- which function(s) needs to be rewritten to make it so? -- Can you tell/guess which function(s) is the problem just by looking at the code below? -- If so, can you explain what the strategy for doing so is? notQuiteRight = takeWhile (not . blank) <$> ( sequence . repeat $ echo ) echo = do l <- getLine putStrLn l return l -- this seems to work... is there a way to make it work Applicatively, with lifted takeWhile? seemsToWork = sequenceWhile_ (not . blank) (repeat echo) sequenceWhile_ p [] = return () sequenceWhile_ p (mx:mxs) = do x <- mx if p x then do sequenceWhile_ p mxs else return () blank x = "" == x