list.fs

        [<CompiledName("SplitAt")>]
        let splitAt (n: int) (list: 'T list) = Microsoft.FSharp.Primitives.Basics.List.splitAt n list

local.fs

    let rec splitAtFreshConsTail cons n l = 
        match l with
        | [] -> 
            if n <> 0 then failwith "insufficient length" 
            else 
            setFreshConsTail cons []
            l
        | x::xs ->
            if n = 0 then
                setFreshConsTail cons []
                xs
            else
                let cons2 = freshConsNoTail x
                setFreshConsTail cons cons2
                splitAtFreshConsTail cons2 (n - 1) xs

    let splitAt n l = 
        if n = 0 then [], l
        else
        match l with
        | []  -> failwith "insufficient length"
        | [_] -> if n = 1 then l, []  else failwith "insufficient length"
        | x::xs ->
            if n = 1 then [x], xs
            else
            let cons = freshConsNoTail x
            let tail = splitAtFreshConsTail cons (n - 1) xs
            cons, tail