[plt-scheme] Tip: installing PLAI Scheme in DrScheme 4.2

i  tool same or similar error i dont remember whem try to debug.When you
write (require blah..) it install programming and intepratation
application.You can choose plai scheme from chhose language.

On Sun, Aug 16, 2009 at 6:12 AM, Eli Barzilay <eli at barzilay.org> wrote:

> On Aug 16, Xingzhi Pan wrote:
> > A quick question to Shriram: I installed PLT 4.2.1 a few days ago and ran
> > (require (planet plai/plai:1:3)).
> >
> > Then upon this code in the PLAI book, PLT fired an error saying "expand:
> > unbound identifier in module in: num"
> >
> > (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)))])]))
> >
> > Is the reader supposed to write num (and add/sub) to make everything
> > work then?
>
> Yes -- you need to write the AE type definition, which defines `num'
> and the other constructors.
>
> --
>          ((lambda (x) (x x)) (lambda (x) (x x)))          Eli Barzilay:
>                    http://barzilay.org/                   Maze is Life!
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