4.22 Exercise 4.22

Adding support for let expressions in this new analyzing interpreter is nearly trivial, because previously we supported them by transforming them into a form we already supported – namely, that of an immediately invoked anonymous function.

(define (analyze exp)

(cond ((self-evaluating? exp)

(analyze-self-evaluating exp))

((quoted? exp) (analyze-quoted exp))

((variable? exp) (analyze-variable exp))

((assignment? exp) (analyze-assignment exp))

((definition? exp) (analyze-definition exp))

((if? exp) (analyze-if exp))

((lambda? exp) (analyze-lambda exp))

((begin? exp) (analyze-sequence (begin-actions exp)))

((cond? exp) (analyze (cond->if exp)))

((let? exp) (analyze (let->combination exp)))

((application? exp) (analyze-application exp))

(else

(error "Unknown expression type -- ANALYZE" exp))))

I say almost trivial because scan-out-defines does not work immediately like this, since the procedure has already been analyzed at the time when it is called. TODO: Remove this limitation...