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Operators.( <| )<'T,'U> Function (F#)

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

Applies a function to a value, the value being on the right, the function on the left.

Namespace/Module Path: Microsoft.FSharp.Core.Operators

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


// Signature:
( <| ) : ('T -> 'U) -> 'T -> 'U

// Usage:
func <| arg1


func Type: 'T -> 'U

The function.

arg1 Type: 'T

The argument.

Return Value

The function result.


The function is referred to as the backward or reverse pipe operator.


The following example demonstrates the use of the <| operator.

let append1 string1 = string1 + ".append1"
let append2 string1 = string1 + ".append2"

let result1 = append1 <| "abc"
printfn "append1 <| \"abc\" gives %A" result1

// Reverse pipelines require parentheses.
let result2 :string = append2 <| (append1 <| "abc")
printfn "result2: %A" result2

// Reverse pipelines can be used to eliminate the need for
// parentheses in some expressions.
raise <| new System.Exception("A failure occurred.")


append1 &lt;| "abc" gives "abc.append1"
result2: "abc.append1.append2"


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

Core.Operators Module (F#)

Microsoft.FSharp.Core Namespace (F#)

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