AWOL message?
- To: mathgroup at smc.vnet.net
- Subject: [mg16634] AWOL message?
- From: Tom Burton <tburton at brahea.com>
- Date: Fri, 19 Mar 1999 12:53:54 -0500
- Sender: owner-wri-mathgroup at wolfram.com
-------------------------------- On 16 Mar 1999 06:20:43 -0500, Jack Goldberg <jackgold at math.lsa.umich.edu> wrote: >...My main purpose in using Mathematica is help students learn mathematics. >So for my purposes the fact that Mathematica evaluates everything in sight >is a major drawback... > >What say yo'all? Having arrived at Mathematica from Fortran and C, I expect full evaluation. Most of my functions are designed to produce atomic output and need full evaluation. I suspect that, on balance, single-step evaluation would bug me. In the explanatory material that complements these functions, I want more control over evaluation. There I create many more rules (a->b) than definitions (a=b). A rule applied with ReplaceAll (expr /. rule) is essentially a single-step evaluation, isn't it? (Provided, of course, that the result of the evaluation does not include a defined expression). I agree with Jack Goldberg that restraining the evaluation of defined symbols with Hold* or Unevaluated can be clumsy and occasionally overwhelming--I see myself trying to hold back a tide of evaluation with a spoon. The two examples he supplied suggest a common strategy: (1) Wrap the entire expression in HoldForm (2) Create rules a->b to transform the expression as desired. * (3) Reach into the held expression with ReplaceAll to apply the rules. (See sections 2.3 and 2.4 of The Mathematica Book.) * In place of a or b, you might need HoldPattern[a] or Holdform[b]. Clumsy. Mathematica follows a small number of simple conventions governing evaluation. They don't fit my needs all the time, but at least I can remember what they are and deal with them. In another part of this thread, Dave Withoff comments that, "Even in systems like Lisp or Macsyma, which are nominally designed around single-step evaluation, most such evaluations happen automatically." Most? Such? Ugh. More conventions to remember. Spare me! Thomas E. Burton 353 Sanford Road Brahea, Inc. Encinitas CA 92024-1508 tburton at brahea.com 760/436-7436