Hey Richard,
I had to make a change to tags. They are now functions and functions
of 0-arity require unit () to be applied to them. "Constructing" a Nil
is now like:
Nil ()
I usually do something like this though:
let nil = Nil ()
Which is annoying. That's probably something that the compiler should do... :)
I pushed a change that updates the code to something that should work
(still commented out).