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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)

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

// Usage:
Seq.head source

source

Type: seq<'T>

The input sequence.

Exception

Condition

ArgumentException

Thrown when the input does not have any elements.

ArgumentNullException

Thrown when the input sequence is null.

The first element of the sequence.

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.

The following code shows how to use Seq.head.

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

Output

1

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

F# Core Library Versions

Supported in: 2.0, 4.0, Portable

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