Use cases for functor/applicative/monad instances for functions : <p>Haskell has <code>Functor</code>, <code>Applicative</code> and <code>Monad</code> instances defined for functions (specifically the partially applied type <code>(-&gt;) a</code>) in the standard library, built around function composition.</p>

<p>Understanding these instances is a nice mind-bender exercise, but my question here is about the practical uses of these instances. I'd be happy to hear about realistic scenarios where folks used these for some practical code.</p>
