Question

I am having trouble with the following F sharp function:

let compare (a:int option list) (b:int option list) =         
let r =
    if a.Tail = [None] && b.Tail = [None] then 
        [None]
    elif a.Tail = [None] then
        [b.Head;None]
    elif b.Tail = [None] then
        [a.Head; None]
    else
        if a=b then
            a
        else
           [None]
r

When I run it with the following arguments

compare [Some 1] [Some 0]

the answer is

[null] 

instead of

[None]

Can somebody explain why; Thank you!

Answer 1

Is the way it is displayed but in fact the value is None.
If you try this

Option.isNone  ( ( compare [Some 1] [Some 0] ).[0] ) ;;

You get

val it : bool = true