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

Article
2013-02-04

Returns the first element of the sequence.

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

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

// 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 does not have any elements.
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

The following code shows how to use Seq.head.

let headItem = Seq.head [| 1 .. 10 |]
printfn "%d" headItem

Output

Platforms

Windows 7, Windows Vista SP2, Windows XP SP3, Windows XP x64 SP2, Windows Server 2008 R2, Windows Server 2008 SP2, Windows Server 2003 SP2

Version Information

F# Runtime

Supported in: 2.0, 4.0

Silverlight

Supported in: 3

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