Applicative functor

An applicative functor has more structure than a functor but less than a monad. See the Haddock docs for Control.Applicative.

It has turned out that many applications do not require monad functionality but only those of applicative functors. Monads allow you to run actions depending on the outcomes of earlier actions.

do text <- getLine
   if null text
     then putStrLn "You refuse to enter something?"
     else putStrLn ("You entered " ++ text)

This is obviously necessary is some cases, but in other cases it is disadvantageous.

Some advantages of Applicative:

• Code that uses only on the Applicative interface are more general than ones uses the Monad interface, because there are more applicative functors than monads.
• Programming with Applicative has a more applicative/functional feel. Especially for newbies, it may encourage functional style even when programming with effects. Monad programming with do notation encourages a more sequential & imperative style.