list.iter2['t1,'t2]-function-[fsharp].md

title	List.iter2<'T1,'T2> Function (F#)
description	List.iter2<'T1,'T2> Function (F#)
keywords	visual f#, f#, functional programming
author	dend
manager	danielfe
ms.date	05/16/2016
ms.topic	language-reference
ms.prod	visual-studio-dev14
ms.technology	devlang-fsharp
ms.assetid	54b3700b-9b7a-46be-8dba-fbdeef5b5353

List.iter2<'T1,'T2> Function (F#)

Applies the given function to two lists simultaneously. The lists must have equal lengths.

Namespace/Module Path: Microsoft.FSharp.Collections.List

Assembly: FSharp.Core (in FSharp.Core.dll)

Syntax

// Signature:
List.iter2 : ('T1 -> 'T2 -> unit) -> 'T1 list -> 'T2 list -> unit

// Usage:
List.iter2 action list1 list2

Parameters

action Type: 'T1 -> 'T2 ->unit

The function to apply to pairs of elements from the input lists.

list1 Type: 'T1list

The first input list.

list2 Type: 'T2list

The second input list.

Exceptions

Exception	Condition
ArgumentException	Thrown when the input lists differ in length.

Remarks

This function is named Iterate2 in compiled assemblies. If you are accessing the function from a language other than F#, or through reflection, use this name.

Example

The following code example illustrates the use of List.iter2 and compares its behavior with related functions.

[!code-fsharpMain]

Output

List.iter: element is 1
List.iter: element is 2
List.iter: element is 3
List.iteri: element 0 is 1
List.iteri: element 1 is 2
List.iteri: element 2 is 3
List.iter2: elements are 1 4
List.iter2: elements are 2 5
List.iter2: elements are 3 6
List.iteri2: element 0 of list1 is 1 element 0 of list2 is 4
List.iteri2: element 1 of list1 is 2 element 1 of list2 is 5
List.iteri2: element 2 of list1 is 3 element 2 of list2 is 6

Platforms

Windows 8, Windows 7, Windows Server 2012, Windows Server 2008 R2

Version Information

F# Core Library Versions

Supported in: 2.0, 4.0, Portable

See Also

Collections.List Module (F#)

Microsoft.FSharp.Collections Namespace (F#)