Step three in creating a fold over a BinomialHeap

BinomialHeap fold step 3.fs

static member private foldHeapStep3 nodeF leafV (h : list<BinomialTree<'a>>) = 

    let rec loop (h : list<BinomialTree<'a>>) cont =
        match h with
        | Node(_, a, [])::[] -> loop []  (fun lacc ->  
                                loop [] (fun racc -> 
                                cont (nodeF a lacc racc)))
        | Node(_, a, h')::[] -> loop h'  (fun lacc ->  
                                loop [] (fun racc -> 
                                cont (nodeF a lacc racc))) 
        | Node(_, a, [])::tl -> loop []  (fun lacc ->  
                                loop tl (fun racc ->
                                cont (nodeF a lacc racc))) 
        | Node(_, a, h')::tl -> loop h'  (fun lacc ->  
                                loop tl (fun racc -> 
                                cont (nodeF a lacc racc))) 
        | _ -> failwith "can't get here"
           
    loop h (fun x -> x)

static member private inOrderStep3 (h : list<BinomialTree<'a>>) = (BinomialHeap.foldHeap (fun x l r acc -> l (x :: (r acc))) (fun acc -> acc) h) [] 

This will now fail when an empty list is passed through the loop, showing we now have a "null" pattern for the continuation identity function.