On Wed, Oct 31, 2012 at 10:44 PM, Daniel Trstenjak < daniel.trstenjak@gmail.com> wrote:
(<||>) :: Monad m => m Bool -> m Bool -> m Bool (<||>) m1 m2 = do r1 <- m1 if r1 then return True else m2
We can do some algebraic simplification, using the law *if P then True else Q *is same as *P || Q* : (<||>) m1 m2 = do r1 <- m1 r2 <- m2 return (r1 || r2) Which reminds me of the definition of liftM2 (from Control.Monad): liftM2 f m1 m2 = do { x1 <- m1; x2 <- m2; return (f x1 x2) } And so we can golf down to: (<||>) = liftM2 (||) Now, instead of using liftM2 from Control.Monad, I could as well use liftA2 from Control.Applicative : (<||>) = liftA2 (||) So my questions to the experts: 1> Are these equivalent or am I missing something? 2> Any thumb rules on when to use Control.Monad and when to use Control.Applicative? Rusi -- http://blog.languager.org