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.<br><br><div class="gmail_quote"> On Sun, Aug 16, 2009 at 6:12 AM, Eli Barzilay <span dir="ltr"><<a href="mailto:eli@barzilay.org">eli@barzilay.org</a>></span> wrote:<br><blockquote class="gmail_quote" style="border-left: 1px solid rgb(204, 204, 204); margin: 0pt 0pt 0pt 0.8ex; padding-left: 1ex;"> <div class="im">On Aug 16, Xingzhi Pan wrote:<br> > A quick question to Shriram: I installed PLT 4.2.1 a few days ago and ran<br> > (require (planet plai/plai:1:3)).<br> ><br> > Then upon this code in the PLAI book, PLT fired an error saying "expand:<br> > unbound identifier in module in: num"<br> ><br> > (define (parse sexp)<br> > (cond<br> > [(number? sexp) (num sexp)]<br> > [(list? sexp)<br> > (case (first sexp)<br> > [(+) (add (parse (second sexp))<br> > (parse (third sexp)))]<br> > [(-) (sub (parse (second sexp))<br> > (parse (third sexp)))])]))<br> ><br> > Is the reader supposed to write num (and add/sub) to make everything<br> > work then?<br> <br> </div>Yes -- you need to write the AE type definition, which defines `num'<br> and the other constructors.<br> <font color="#888888"><br> --<br> ((lambda (x) (x x)) (lambda (x) (x x))) Eli Barzilay:<br> <a href="http://barzilay.org/" target="_blank">http://barzilay.org/</a> Maze is Life!<br> </font><div><div></div><div class="h5">_________________________________________________<br> For list-related administrative tasks:<br> <a href="http://list.cs.brown.edu/mailman/listinfo/plt-scheme" target="_blank">http://list.cs.brown.edu/mailman/listinfo/plt-scheme</a><br> </div></div></blockquote></div><br>