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List.forall2<'T1,'T2> Function (F#)

Den Delimarsky|Last Updated: 8/18/2017
2 Contributors

Tests if all corresponding elements of the lists satisfy the given predicate pairwise. The lists must have equal lengths.

Namespace/Module Path: Microsoft.FSharp.Collections.List

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


// Signature:
List.forall2 : ('T1 -> 'T2 -> bool) -> 'T1 list -> 'T2 list -> bool

// Usage:
List.forall2 predicate list1 list2


predicate Type: 'T1 -> 'T2 ->bool

The function to test the input elements.

list1 Type: 'T1list

The first input list.

list2 Type: 'T2list

The second input list.


ArgumentExceptionThrown when the input lists differ in length.

Return Value

true if all of the pairs of elements satisfy the predicate. Otherwise, returns false.


The predicate is applied to matching elements in the two collections. If any application returns false then the overall result is false and no further elements are tested. Otherwise, if one collection is longer than the other then the System.ArgumentException exception is raised. Otherwise, true is returned.

This function is named ForAll2 in compiled assemblies. If you are accessing the function from a .NET language other than F#, or through reflection, use this name.


let listEqual list1 list2 = List.forall2 (fun elem1 elem2 -> elem1 = elem2) list1 list2
printfn "%b" (listEqual [0; 1; 2] [0; 1; 2])
printfn "%b" (listEqual [0; 0; 0] [0; 1; 0])




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.List Module (F#)

Microsoft.FSharp.Collections Namespace (F#)

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