"I want to understand vau"

Apparently, youse people don't know the R^-1RK by heart yet.

Vau is just like lambda, except it doesn't evaluate its arguments, and receives the lexical environment in which it is called.

Vau's syntax is (vau operands environment . body).

Lambda's syntax is (lambda arguments . body).

((vau x e x) foo) ==> (foo)

((vau x e e) foo) ==> #[environment]

You can also destructure the operands:

((vau (x y z) e z) foo bar baz) ==> baz

And if you want to get at the actual value of an operand, you use eval, which takes a form and an environment as parameters:

(def msg "Hello world!")

((vau (x) e (eval x e)) msg) ==> "Hello world!"

Note: you can try out these expressions at the Virtua REPL.