Anonymous function
In computer science and mathematics, an anonymous function is a function that has no name. Usually, a function is written like: [math]\displaystyle{ f(x) = x^2 - x + 42 }[/math]. It can be written anonymously as [math]\displaystyle{ x \rightarrow x^2 - x + 42 }[/math] These are used in functional programming languages and other programming languages with support for anonymous functions (those which support 1st class functions).
Examples in some programming languages
Python
<source lang="python"> (lambda x: (lambda y: x * y)) </source>
The above code can be executed as a function:
<source lang="python"> >>>(lambda x: (lambda y: x * y))(3)(4) 12 </source>
Haskell
<source lang="haskell"> \x -> \y -> x * y </source>
The above code can be executed as a function:
<source lang="haskell"> (\x -> \y -> x * y) 3 4 </source>
The function can also be written in point-free (tacit) style: <source lang="haskell"> (*) </source>
Standard ML
Not curried: <source lang="ocaml"> fn (x, y) => x * y
(* or *)
(op * ) </source>
Curried: <source lang="ocaml"> fn x => fn y => x * y </source>
JavaScript
<source lang="javascript"> // uncurried function(x, y) {
return x * y;
}
// curried function(x) {
return (function(y)
{
return x * y;
});
} </source>
Scheme
<source lang="scheme">
- uncurried
(lambda (x y) (* x y))
- usage
((lambda (x y) (* x y)) 3 4) (* 3 4)
- curried
(lambda (x) (lambda (y) (* x y)))
- usage
(((lambda (x) (lambda (y) (* x y))) 3) 4) </source>
C++ 11
Not curried: <source lang="cpp"> [](int x, int y)->int { return x * y; }; </source> Curried: <source lang="cpp"> [](int x) { return [=](int y)->int { return x * y; }; }; </source>
C++ Boost
<source lang="cpp"> _1 * _2 </source> Note: What you need to write boost lambda is to include <boost/lambda/lambda.hpp> header file, and using namespace boost::lambda, i.e. <source lang="cpp">
- include <boost/lambda/lambda.hpp>
using namespace boost::lambda; </source>
You can call it as: (_1 * _2)(3, 4) to get 12.