seq.head['t]-function-[fsharp].md

title	Seq.head<'T> Function (F#)
description	Seq.head<'T> 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	a5342ecf-d84d-422c-b9c5-cd23c2322461

Seq.head<'T> Function (F#)

Returns the first element of the sequence.

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

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

Syntax

// Signature:
Seq.head : seq<'T> -> 'T

// Usage:
Seq.head source

Parameters

source Type: seq<'T>

The input sequence.

Exceptions

Exception	Condition
ArgumentException	Thrown when the input sequence is empty.
ArgumentNullException	Thrown when the input sequence is null.

Return Value

The first element of the sequence.

Remarks

The first element of the source sequence is evaluated at each call. To avoid this reevaluation, you can create a cached version of a sequence by calling Seq.cache.

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

Example

[!code-fsharpMain]

Output

1

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.Seq Module (F#)

Microsoft.FSharp.Collections Namespace (F#)