>>82
If you've read SICP, you would know that
THE SUSSMAN does advocate data abstraction. What's so impossible about (define (type-constructor a b) .... )? Of course it doesn't have some benefits the anal type system of Haskell has, and you actually have to document the ``type'''s definition as well as the functions' type to make sense out of your shits, but it is exactly what Lithpers normally do. Hint: Lithpers usually avoid using conses if possible, because
EFFICIENCY.