title: What exactly does "effectful" mean
body: <p>Time and again I read the term <em>effectful</em>, but I am still unable to give a clear definition of what it means. I assume the correct context is effectful <em>computations</em>, but I've also seen the term effectful <em><a href="https://stackoverflow.com/questions/24467803/how-to-handle-side-effect-with-applicative">values</a></em>)</p>
  
  <p>I used to think that effectful means <em>having side effects</em>. But in Haskell there are no side-effects (except to some extent IO). Still there are effectful computations all over the place.</p>
  
  <p>Then I read that monads are used to create effectful computations. I can somewhat understand this in the context of the <code>State</code> Monad. But I fail to see any side-effect in the <code>Maybe</code> monad. In general it seems to me, that Monads which wrap a function-like thing are easier to see as producing side-effects than Monads which just wrap a value.</p>
  
  <p>When it comes to <code>Applicative</code> functors I am even more lost. I always saw applicative functors as a way to <code>map</code> a function with more than one argument. I cannot see any side-effect here. Or is there a difference between <em>effectful</em> and <em>with effects</em>?</p>