Built in equality of lists using a custom comparison function?

Is there a built-in function which does the following?

let rec listsEqual xl yl f =
    match xl, yl with
    | [], [] -> true
    | [], _ | _, [] -> false开发者_StackOverflow中文版
    | xh::xt, yh::yt -> if f xh yh then listsEqual xt yt f else false

Updated, further elaboration: and in general is there any way to tap in to structural comparison but using a custom comparison function?

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List.forall2 : (('a -> 'b -> bool) -> 'a list -> 'b list -> bool)

But it takes f before the lists. You can create your function like this:

let listsEqual x y f =
    if List.length x = List.length y then
        List.forall2 f x y
    else
        false

Remember that List.forall2 assumes the lengths are the same.

---

Concerning Seq.compareWith, you wrote:

not quite, two problems 1) expects the two sequences be of the same type, 2) doesn't short circuit

2) is wrong, the function really does a court-circuit. 1) is true. Take Seq.compareWith from F# library, modify (or remove) the type annotation and it will work for sequences of different types.

[<CompiledName("CompareWith")>]
let compareWith (f:'T1 -> 'T2 -> int) (source1 : seq<'T1>) (source2: seq<'T2>) =
            //checkNonNull "source1" source1
            //checkNonNull "source2" source2
            use e1 = source1.GetEnumerator()
            use e2 = source2.GetEnumerator()
            let rec go () = 
                let e1ok = e1.MoveNext() 
                let e2ok = e2.MoveNext() 
                let c = (if e1ok = e2ok then 0 else if e1ok then 1 else -1) 
                if c <> 0 then c else
                if not e1ok || not e2ok then 0 
                else
                    let c = f e1.Current e2.Current 
                    if c <> 0 then c else
                    go ()
            go()

Now, you can send an email to fsbugs (@ microsoft.com) and ask them to remove the type constraint in the next F# release.