qsort [] = [] qsort (x:xs) = qsort (filter (x <) xs) ++ [x] ++ qsort (filter (x >=) xs)
Note that you can help the reader by making the precedence a bit more obvious: qsort [] = [] qsort (x:xs) = qsort (filter (x <) xs) ++ [x] ++ qsort (filter (x >=) xs) I find that my students can understand this much better than the 1½ liner. Regarding the mapM_ example:
mapM_ (\(n,v) -> putStrLn $ "[" ++ show n ++ "] = " ++ show v) (zip [0..] vs)
To somebody familiar with Haskell, that is as clear as day.
I guess I'm not familiar with Haskell, because I find the paren-counting to be difficult to do in my head (and god knows that I'm familiar with parenthese). Also, I tend to shy away from ($) and (.) and to only use them when I have a list of functions to compose/apply and want to avoid growing the depth of my AST with the length of the list. So I'd probably write the mapM_ example as: mapM_ (\(n,v) -> putStrLn ("[" ++ show n ++ "] = " ++ show v)) (zip [0..] vs) which I find a lot easier to read. Stefan