3 (define (tagged-list? exp tag)
8 (define (make-lambda params body)
9 (cons 'lambda (cons params body)))
12 (tagged-list? expr 'let*))
14 (define (let*-bindings expr) (cadr expr))
15 (define (let*-body expr) (cddr expr))
18 (define (let*->let bindings body)
19 (cond [(empty? bindings) '()]
21 (let ([binding (car bindings)]
22 [rest-bindings (cdr bindings)])
23 (if (empty? rest-bindings)
24 (cons 'let (cons (list binding) body))
25 (cons 'let (cons (list binding) (list (let*->let rest-bindings body))))))]))
29 (define (make-let bindings body)
30 (cons 'let (cons bindings body)))
32 (define (let*->let bindings body)
33 (cond [(empty? bindings) body]
35 (make-let (list (car bindings))
36 (list (let*->let (cdr bindings) body))]))
39 (define (let*->nested-lets exp)
40 (let ([bindings (let*-bindings exp)]
41 [body (let*-body exp)])
42 (let*->let bindings body)))
47 It is enough to add an action for let* expression in eval, as eval
48 gets recursively called for the transformed expressions (assuming that
49 eval has case handlers for let expression whose action is to transform
50 into lambda expression application and eval it).
52 if we add the following action for let* expressions in eval:
54 (eval (let*->nested-lets exp) env)
56 (eval (let-expression) env)
58 (eval (let->combination exp) env)
60 (eval (application exp parameters) env)