| title | Lambda Expressions: The fun Keyword (F#) |
|---|---|
| description | Learn how to use the F# 'fun' keyword to define a lambda expression, which is an anonymous function. |
| keywords | visual f#, f#, functional programming |
| author | cartermp |
| ms.author | phcart |
| ms.date | 05/16/2016 |
| ms.topic | language-reference |
| ms.prod | .net |
| ms.technology | devlang-fsharp |
| ms.devlang | fsharp |
| ms.assetid | e5d3565c-d7cc-433f-a619-886ed92523a7 |
The fun keyword is used to define a lambda expression, that is, an anonymous function.
fun parameter-list -> expressionThe parameter-list typically consists of names and, optionally, types of parameters. More generally, the parameter-list can be composed of any F# patterns. For a full list of possible patterns, see Pattern Matching. Lists of valid parameters include the following examples.
// Lambda expressions with parameter lists.
fun a b c -> ...
fun (a: int) b c -> ...
fun (a : int) (b : string) (c:float) -> ...
// A lambda expression with a tuple pattern.
fun (a, b) -> …
// A lambda expression with a list pattern.
fun head :: tail -> …The expression is the body of the function, the last expression of which generates a return value. Examples of valid lambda expressions include the following:
[!code-fsharpMain]
Lambda expressions are especially useful when you want to perform operations on a list or other collection and want to avoid the extra work of defining a function. Many F# library functions take function values as arguments, and it can be especially convenient to use a lambda expression in those cases. The following code applies a lambda expression to elements of a list. In this case, the anonymous function adds 1 to every element of a list.
[!code-fsharpMain]