MAPn

mapN is a common higher-order function in functional programming used to apply a plain function to multiple values that are wrapped in a context, such as Option, List, Future, or Validation. It lifts a function of N arguments into the context, returning a value wrapped in the same context.

The concept relies on an Apply or Applicative instance for the context. With an Apply, mapN can combine several effectful values without sequencing them, in contrast to monadic binds. The result is obtained by applying the function inside the context to the contained values, yielding a new value in the same context.

In Scala’s Cats library, mapN is often used with the apply syntax. For example, after importing cats.syntax.apply._, (Option(1), Option(2)).mapN(_ + _) yields Some(3). For three values, (Option(1), Option(2), Option(3)).mapN(_ + _ + _).map(_). It can also work with Validation to accumulate errors when the context supports applicative error accumulation, rather than short-circuiting on the first error.

In other languages, similar functionality exists under different names, such as liftA2, liftA3 in Haskell or related libraries, which serve the same purpose: combining multiple applicative values with a function. mapN is specifically useful when you want to apply a function to several independent, context-wrapped values in a single, declarative step.

See also: Applicative, Apply, liftA2, zipWith.