On Mon, Dec 13, 2010 at 7:15 AM, Jacek Generowicz <jacek.generow...@cern.ch> wrote: > -- Is it possible to rewrite code written in this style > > untilQuit = do > text <- getLine > report text > if text == "quit" > then return () > else untilQuit > > -- in a style using higher order functions for abstract iteration? For > -- example, something along these lines: > > untilQuit' = (fmap (takeWhile (/= "quit"))) (sequence $ map (>>= report) > (repeat getLine))
You are asking about standard library functions? Probably, but I think it is cleanest to just write a HOF to encapsulate this pattern. I have used this one before: whileM_ :: (Monad m) => (a -> Bool) -> m a -> m () whileM_ p m = bool (return ()) (whileM p m) . p =<< m bool :: a -> a -> Bool -> a bool t f True = t bool t f False = f untilQuit = whileM_ (/= "quit") (getLine >>= liftM2 (>>) report return) I find a variant of whileM that returns m [a] particularly handy for collecting events in an event loop. Luke _______________________________________________ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
