The two myAction functions below seem to be equivalent and, for this small case, show an interesting economy of code, but being far from a Haskell expert, I have to ask, is the first function as small (code wise) as it could be?
Michael
import Control.Applicative
data Color
= Red
| Blue
| Green
| Yellow
| Orange
| Brown
| Black
| White
deriving (Show, Read, Eq, Enum, Ord, Bounded)
-- myAction :: IO Color
-- myAction = getLine
-- >>= \str -> return (read str :: Color)
|
First, you don't need the type annotation here. Haskell will infer it from the annotation on myAction. (You also don't need the type on myAction, but that's not important now.)
myAction = getLine >>= \str -> return (read str)
Second, you have the pattern \x -> f (g x), so you can replace the lambda with function composition.
myAction = getLine >>= return . read
Third, there is a standard function liftM, defined in Control.Monad, where liftM f m = m >>= return . f, so
myAction = liftM read getLine
Finally, we expect an instance of Monad to also be an instance of Functor, with fmap = liftM, and we also have f <$> m = fmap f m, so
myAction :: IO Color
myAction = read <$> getLine |