SICP Exercose 4.5, without peeking at others's code

ex45.scm

(define (expand-clauses clauses)
  (if (null? clauses)
      'false                            ; no else clause
      (let ((first (car clauses))
            (rest (cdr clauses)))
       (if (cond-else-clause? first)
            (if (null? rest)
                (sequence->exp (cond-actions first))
                (error "ELSE clause isn't last -- COND->IF"
                       clauese))
            (if (cond=>clause? first)
                (let ((val (car first)))
                  (if val
                      (list (caddr first) val)
                      (make-if (cond-predicate first)
                               (sequence->exp (cond-actions first))
                               (expand-clauses rest)))))))))