Personal tools

Applicative functor

From HaskellWiki

Revision as of 08:00, 5 November 2007 by Conal (Talk | contribs)

Jump to: navigation, search
An applicative functor has more structure than a functor but less than a monad. See the Haddock docs for <div class="inline-code">

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