[plt-scheme] Chapter 1 of Programming Languages: Application and Interpretation Shriram Krishnamurthi

I use DrScheme , I set  it to Advanced Student(may be I didn't do it well),
while it seems the book used something else(I may be wrong too). Could
someone who has read this book before instruct me on what to do? Basically,
how to get the codes snippet of Chapter 1 up and runnig.
(define (parse sexp)
(cond
[(number? sexp) (num sexp)]
[(list? sexp)
(case (first sexp)
[(+) (add (parse (second sexp))
(parse (third sexp)))]
[(-) (sub (parse (second sexp))
(parse (third sexp)))])]))

Regards,
Emeka
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