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Visual F#
Visual F# Development Portal
What's new in Visual F#
Visual F# Guided Tour
Using Visual Studio to Write F# Programs
F# Language Reference
F# Compiler (fsc.exe) Reference
F# Interactive (fsi.exe) Reference
F# Core Library Reference
Microsoft.FSharp.Collections Namespace
Array Module
Array2D Module
Array3D Module
Array4D Module
ComparisonIdentity Module
HashIdentity Module
List Module
list<'T> Type Abbreviation
List<'T> Union
Map<'Key,'Value> Class
Collections.Map Module
Collections.ResizeArray<'T> Type Abbreviation
Collections.Seq Module
Seq.append<'T> Function
Seq.average<^T> Function
Seq.averageBy<'T,^U> Function (F#)
Seq.cache<'T> Function (F#)
Seq.cast<'T> Function (F#)
Seq.choose<'T,'U> Function (F#)
Seq.collect<'T,'Collection,'U> Function (F#)
Seq.compareWith<'T> Function (F#)
Seq.concat<'Collection,'T> Function (F#)
Seq.contains<'T> Functions (F#)
Seq.countBy<'T,'Key> Function (F#)
Seq.delay<'T> Function (F#)
Seq.distinct<'T> Function (F#)
Seq.distinctBy<'T,'Key> Function (F#)
Seq.empty<'T> Type Function (F#)
Seq.exactlyOne<'T> Function (F#)
Seq.exists<'T> Function (F#)
Seq.exists2<'T1,'T2> Function (F#)
Seq.filter<'T> Function (F#)
Seq.find<'T> Function (F#)
Seq.findIndex<'T> Function (F#)
Seq.fold<'T,'State> Function (F#)
Seq.forall<'T> Function (F#)
Seq.forall2<'T1,'T2> Function (F#)
Seq.groupBy<'T,'Key> Function (F#)
Seq.head<'T> Function (F#)
Seq.init<'T> Function (F#)
Seq.initInfinite<'T> Function (F#)
Seq.isEmpty<'T> Function (F#)
Seq.item<'T> Function (F#)
Seq.iter<'T> Function (F#)
Seq.iteri<'T> Function (F#)
Seq.iter2<'T1,'T2> Function (F#)
Seq.last<'T> Function (F#)
Seq.length<'T> Function (F#)
Seq.map<'T,'U> Function (F#)
Seq.mapi<'T,'U> Function (F#)
Seq.map2<'T1,'T2,'U> Function (F#)
Seq.max<'T> Function (F#)
Seq.maxBy<'T,'U> Function (F#)
Seq.min<'T> Function (F#)
Seq.minBy<'T,'U> Function (F#)
Seq.nth<'T> Function (F#)
Seq.ofArray<'T> Function (F#)
Seq.ofList<'T> Function (F#)
Seq.pairwise<'T> Function (F#)
Seq.pick<'T,'U> Function (F#)
Seq.readonly<'T> Function (F#)
Seq.reduce<'T> Function (F#)
Seq.scan<'T,'State> Function (F#)
Seq.singleton<'T> Function (F#)
Seq.skip<'T> Function (F#)
Seq.skipWhile<'T> Function (F#)
Seq.sort<'T> Function (F#)
Seq.sortBy<'T,'Key> Function (F#)
Seq.sum<^T> Function (F#)
Seq.sumBy<'T,^U> Function (F#)
Seq.tail<'T> Function (F#)
Seq.take<'T> Function (F#)
Seq.takeWhile<'T> Function (F#)
Seq.toArray<'T> Function (F#)
Seq.toList<'T> Function (F#)
Seq.tryFind<'T> Function (F#)
Seq.tryFindIndex<'T> Function (F#)
Seq.tryPick<'T,'U> Function (F#)
Seq.truncate<'T> Function (F#)
Seq.unfold<'State,'T> Function (F#)
Seq.where<'T> Function (F#)
Seq.windowed<'T> Function (F#)
Seq.zip<'T1,'T2> Function (F#)
Seq.zip3<'T1,'T2,'T3> Function (F#)
Collections.seq<'T> Type Abbreviation
Collections.Set<'T> Class
Collections.Set Module
Microsoft.FSharp.Control Namespace (F#)
Microsoft.FSharp.Core Namespace (F#)
Microsoft.FSharp.Core.CompilerServices Namespace (F#)
Microsoft.FSharp.Data Namespace
Microsoft.FSharp.Linq Namespace (F#)
Microsoft.FSharp.NativeInterop Namespace (F#)
Microsoft.FSharp.Quotations Namespace (F#)
Microsoft.FSharp.Reflection Namespace (F#)
System Namespace (F#)
System.Collections Namespace (F#)
System.Numerics Namespace (F#)
System.Threading Namespace (F#)
Visual F# Samples and Walkthroughs
Type Providers (F#)
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Seq.head<'T> Function (F#)

Den Delimarsky|Last Updated: 8/18/2017
|
1 Contributor

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

ExceptionCondition
ArgumentExceptionThrown when the input sequence is empty.
ArgumentNullExceptionThrown 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


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

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#)

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