The source of the page has a few hidden gems, including:

    <SCRIPT LANGUAGE='SCHEME'>
    (define (eval exp env)
      (cond ((self-evaluating? exp) exp)
            ((variable? exp) (lookup-variable-value exp env))
            ((quoted? exp) (text-of-quotation exp))
            ((assignment?  exp) (eval-assignment exp env))
            ((definition? exp) (eval-definition exp env))
            ((if? exp) (eval-if exp env))
            ((lambda? exp) (make-procedure (lambda-parameters exp) (lambda-body exp) env))
            ((begin? exp) (eval-sequence (begin-actions exp) env))
            ((cond? exp) (eval (cond->if exp) env))
            ((application? exp)  (apply (eval (operator exp) env) (list-of-values (operands exp) env)))
            (else (error "Common Lisp or Netscape Navigator 4.0+ Required" exp))))
    </SCRIPT>