In many programming languages, map is the name of a higher-order function that applies a given function to a sequence of elements (such as a list) and returns a sequence of results.
For example, if we define a function square as follows:
square x = x * x
Then calling (map square [1,2,3,4,5]) will return [1,4,9,16,25].
Map itself may be defined recursively as:
map f [] = [] map f (x:xs) = f x : map f xs
The map function is especially common in functional programming languages, but some high-level procedural languages support it as well, and in others it may be defined.
In Common Lisp, there is a whole family of map-like functions. The one that corresponds to the behaviour described here is called mapcar.
In C++'s standard library, the map function is called transform
Haskell's Functor class
In the Haskell programming language, map is generalized to a polymorphic function called fmap using the Functor type class. For every Functor instance, fmap must be defined such that it obeys by the Functor laws:
fmap id = idfmap (f . g) = fmap f . fmap g