<html> <head> <meta content="text/html; charset=ISO-8859-1" http-equiv="Content-Type"> </head> <body bgcolor="#FFFFFF" text="#000000"> <div class="moz-cite-prefix">Op 30-6-2012 1:38, Neil Van Dyke schreef: </div> <blockquote cite="mid:4FEE3C65.6070809@neilvandyke.org" type="cite">Stephen Bloch wrote at 06/29/2012 06:01 PM: <blockquote type="cite">Either you introduce this stuff much better than I do, or your students are much sharper. </blockquote> For the possible benefit of any students reading, I think someone say it, rather than leave it implied: Or the difference could be an isolated effect of, say, some subtle difference in how one concept was first introduced in their respective educations, not a reflection on the instruction or students overall. Aside: I think students are much the same everywhere, and most all students have potential to be good at this stuff.  But learning this stuff well requires a lot of work, and I think students generally do need to have sufficient sense that they're ``sharp,'' so that they stick with it and put in the necessary work.  Or, there is another category of person, who sees themself as slow but determined; that will also lead to learning the stuff, if the self image gets them to put in the necessary work.  (However, the ones who are self-assured and yet who don't do the learning work... they are doomed to be dim and to have few job options other than some kind of politician.) Neil V. ____________________  Racket Users list:  <a class="moz-txt-link-freetext" href="http://lists.racket-lang.org/users">http://lists.racket-lang.org/users</a> </blockquote> Im rereading the chapter and I think I found a piece of the puzzle. In the chapter there is a mention of this : <table class="RktBlk" cellspacing="0"> <tbody> <tr> <td>; A <a name="(tech._mix._sig)"></a>SIGS (short for “space invader game state”) is one of: </td> </tr> <tr> <td>; – (make-aim <a class="techoutside" href="#%28tech._mix._ufo%29" pltdoc="x">UFO</a> <a class="techoutside" href="#%28tech._mix._tank%29" pltdoc="x">Tank</a>)</td> </tr> <tr> <td>; – (make-fired <a class="techoutside" href="#%28tech._mix._ufo%29" pltdoc="x">UFO</a> <a class="techoutside" href="#%28tech._mix._tank%29" pltdoc="x">Tank</a> <a class="techoutside" href="#%28tech._mix._missile%29" pltdoc="x">Missile</a>)</td> </tr> </tbody> </table> I can do the same for my problem. ; A Vanimal is one of : ; - (make-Vcat ( x happiness) ;   (make-Vcham ( x happiness) So Vanimal is not a struct but strictly a name. Am I on the right track. Roelof </body> </html>