Newsgroups: comp.lang.logo Path: news.media.mit.edu!bloom-beacon.mit.edu!gatech!news-feed-2.peachnet.edu!umn.edu!dialup-2-132.gw.umn.edu!user From: moren004@maroon.tc.umn.edu (Andres F. Moreno) Subject: Variables (was: Brian Harvey's text) Message-ID: Followup-To: comp.lang.logo Sender: news@news2.cis.umn.edu (Usenet News Administration) Nntp-Posting-Host: dialup-2-132.gw.umn.edu Organization: University of Minnesota Date: Mon, 20 Dec 1993 02:46:50 GMT Lines: 38 This thread has been discussing something which all of us know at heart: programming is a non-trivial proposition. Rehashing prehistoric lore, people sincerely thought programmers would disappear with the invention of FORTRAN! I do agree with larry that a conceptual framework is essential. The people who think usually do best at formal tasks like programming. Something as simple as the notion of a variable has to be understood clearly. Because of the pervasive effects of Von Neumann architectures, teachers usually talk about variables in terms of memory cells holding a number or a letter (the value of the variable). Why not think of variables as a pair (name, value) with the property that one can access the value of the variable by, say, placing a ":" as a prefix? This takes all the mystery out of the MAKE statement! [I know that a sizable group of people in the AI comunity already teach this way, but having been around the block, I know that many teachers still cling to EXTERNAL constraints, such as the architecture of the machine their programs happen to be running on]. Now, armed with the concept of a variable, one can proceed to simulate Von Neumann and *Non-von Neumann* architectures! This is what LOGO is all about! Giving people the expressive power to explore complicated things! For a non-trivial example, check out the Scheme book by Abelson and Sussman, _Structure_and_Interpretation_of_Computer_Programs, p. 83. This gives you a way to implement car and cons (list building operations) without any notion of a memory cell! My warmest regards to teachers, who have to do 101 things. Teaching computer programming is perhaps the most difficult of the 101. -- Andres F. Moreno --Don't call us, we'll call you!!! Department of Spanish and Portuguese University of Minnesota, Mpls 55455 email address: moren004@maroon.tc.umn.edu **************************************************************************