original.name="Reference_Invalid_6"
======
>>> main.whiley
type LinkedList is null | &{ int data, LinkedList next }

method append(LinkedList head, LinkedList tail) -> LinkedList:
    if head is null:
        return tail
    else if tail is null:
        return head
    else:
        // quickcheck should catch this
        assert head != tail
        //
        return new { data: head->data, next: append(head->next,tail) }

public export method test():
    LinkedList l1 = null
    LinkedList l2 = new { data: 2, next: l1 }
    LinkedList l3 = new { data: 3, next: l1 }
    // Tests
    LinkedList r1 = append(l2,l1)
    LinkedList r2 = append(l1,l2)
    assume r1 == l2
    assume r2 == l2
    LinkedList r3 = append(l2,l3)    
    assume !(r3 is null)
    LinkedList r4 = r3->next
    assume !(r4 is null)
    assume r3->data == 2 && r4->data == 3 && r4->next == null
    // finally, break it
    LinkedList r5 = append(l2,l2)
---
E705 main.whiley 10,15:26
E722 main.whiley 10,15:26