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

Evaluates the equivalent of List.forall for an option type.

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

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

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

// Usage:
forall predicate option

Parameters

• 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.

Return Value

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

Remarks

The expression forall p inp evaluates to match inp with None -> true | Some x -> p x.

This function is named ForAll 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 illustrates the use of Option.forall.

let isEven opt =
    Option.forall (fun elem -> elem % 2 = 0) opt
printfn "%b" <| isEven (Some(2))
printfn "%b" <| isEven None
printfn "%b" <| isEven (Some(1))

// Use this function with an array of int options.
let forAllOptions function1 = List.forall (fun opt -> Option.forall function1 opt)
let list1 = [ for i in 1 .. 10 do yield Some(i) ]
let list2 = [ for i in 1 .. 10 do yield if (i % 2) = 0 then Some(i) else None ]
let list3 = [ for i in 1 .. 10 do yield if (i % 2) = 1 then Some(i) else None ]
let evalList list = printfn "%b" <| forAllOptions (fun value -> value % 2 = 0) list
let lists = [ list1; list2; list3 ]
List.iter evalList lists

Output

true
true
false
false
true
false

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

See Also

Reference

Core.Option Module (F#)

Microsoft.FSharp.Core Namespace (F#)