Java vs. rex
lThe analog to function in rex is method in Java.  Functions are applied as aFunction(x, y, z), while methods are applied like x.aMethod(y, z).

lArgument and return types must be declared in Java, not in rex.

lBoth allow recursion.

lAll of the underlying functionality in rex is implementable.

lThink of rex lists as your abstraction, use Java to implement it.
principal argument (an object)