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Option.exists<'T> Function (F#)

Evaluates the equivalent of List.exists for an option.

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

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

// Signature:
exists : ('T -> bool) -> 'T option -> bool

// Usage:
exists predicate option

predicate

Type: 'T -> bool

A function that evaluates to a Boolean when given a value from the option type.

option

Type: 'T option

The input option.

Returns false if the option is None, otherwise it returns the result of applying the predicate to the option value.

The expression exists p inp evaluates to match inp with None -> false | Some x -> p x.

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

The following code illustrates the use of Option.exists.


let isValue opt value =
    Option.exists (fun elem -> elem = value) opt
let testOpt1 = Some(10)
let testOpt2 = Some(11)
let testOpt3 = None
printfn "%b" <| isValue testOpt1 10
printfn "%b" <| isValue testOpt2 10
printfn "%b" <| isValue testOpt3 10


Output

true
false
false

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

F# Runtime

Supported in: 2.0, 4.0

Silverlight

Supported in: 3

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