Answer till 4.27

misc/evaluator.scm

@@ -4,6 +4,7 @@
         ((quoted? exp) (text-of-quotation exp))
         ((assignment? exp) (eval-assignment exp env))
         ((definition? exp) (eval-definition exp env))
+        ((unless? exp) (eval (unless->combination exp) env))
         ((if? exp) (eval-if exp env))
         ((lambda? exp)
          (make-procedure (lambda-parameters exp)
@@ -108,6 +109,7 @@
 (define (make-lambda parameters body)
   (cons 'lambda (cons parameters body)))
 
+(define (unless? exp) (tagged-list? exp 'unless))
 (define (if? exp) (tagged-list? exp 'if))
 (define (if-predicate exp) (cadr exp))
 (define (if-consequent exp) (caddr exp))
@@ -244,8 +246,12 @@
         (list 'cons cons)
         (list 'null? null?)
         (list 'display display)
+        (list 'equal? equal?)
+        (list 'newline newline)
         (list '= =)
         (list '+ +)
+        (list '* *)
+        (list '/ /)
         (list '- -)
         (list '< <)
         ;;<more primitives>
@@ -299,6 +305,12 @@
                      '<procedure-env>))
       (display object)))
 
+(define (eval-verbose exp env)
+  (let ((output (eval exp env)))
+      (user-print output) (newline)
+      output))
+
+
 (define the-global-environment (setup-environment))
 
 ;(driver-loop)