Functor (functional programming)

rdf:langString Functor (functional programming)

rdf:langString In functional programming, a functor is a design pattern inspired by the definition from category theory, that allows for a generic type to apply a function inside without changing the structure of the generic type. This idea is encoded in Haskell using type class class Functor f where fmap :: (a -> b) -> f a -> f b with conditions called functor laws, fmap id = idfmap (g . h) = (fmap g) . (fmap h) In Scala are used trait Functor[F[_]] { def map[A,B](a: F[A])(f: A => B): F[B]} Simple examples of this are Option and collection types. Functors are very useful in modeling to apply a function to computations that did not yet finish. Functors form a base for more complex abstractions like Applicative, Monad, Comonad. In C++, the name functor is commonly used to refer to a function object, even though the ISO/IEC 14882 standard specification itself exclusively uses the latter term.