Exercise 4.1.  Notice that we cannot tell whether the metacircular 
evaluator evaluates operands from left to right or from right to left. 
Its evaluation order is inherited from the underlying Lisp: If the 
arguments to cons in list-of-values are evaluated from left to right, 
then list-of-values will evaluate operands from left to right; and if 
the arguments to cons are evaluated from right to left, then 
list-of-values will evaluate operands from right to left.

Write a version of list-of-values that evaluates operands from left to 
right regardless of the order of evaluation in the underlying Lisp. Also 
write a version of list-of-values that evaluates operands from right to 
left.

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Left to right:

(define (list-of-values exps env)
  (if (no-operands? exps)
      '()
      (let ((first (eval (first-operand exps) env)))
        (cons first (list-of-values (rest-operands exps) env)))))

Right to left:

(define (list-of-values exps env)
  (if (no-operands? exps)
      '()
      (let ((rest (list-of-values (rest-operands exps) env)))
        (cons (eval (first-operand exps) env) rest))))