Also, cons, car, and cdr need not be primitives. They can be built out of lambdas. In Scheme:

  (define (cons x y)
    (lambda (m) (m x y)))

  (define (car z)
    (z (lambda (p q) p)))

  (define (cdr z)
    (z (lambda (p q) q)))

(From https://mitpress.mit.edu/sites/default/files/sicp/full-text/..., exercise 2.4)

Sure. Now to implement consp, all you need is a global list which tracks all lambdas that came from the cons function; if the argument object is eq to anything on that list, then it is a cons! We also now need another primitive: weak pointers. We don't want our global list to prevent otherwise unreferenced cells from being reclaimed.

typecase is going to be fun to develop and optimize, with everything being a lambda.