Trying out the first example in the book
#lang plai
(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)))])]))
I get
<unsaved editor>:4:21: expand: unbound identifier in module in: num
FWIW I have installed the patch on the books webpage and am running Racket 5.01
on Ubuntu.
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