Re: Re: Re: Re: Mathematica language issues

*To*: mathgroup at smc.vnet.net*Subject*: [mg53157] Re: [mg53142] Re: [mg53112] Re: [mg53050] Re: Mathematica language issues*From*: Andrzej Kozlowski <akoz at mimuw.edu.pl>*Date*: Mon, 27 Dec 2004 06:41:27 -0500 (EST)*References*: <200412241058.FAA05777@smc.vnet.net> <200412250900.EAA18524@smc.vnet.net>*Sender*: owner-wri-mathgroup at wolfram.com

I am sure Fred will provide his own answers, but on the principle "the more the merrier" (especially at Christmas) , I thought I would contribute my own comments: On 25 Dec 2004, at 18:00, DrBob wrote: > Fred, > > At several points you made statements I simply don't understand. The > examples clarify what you meant for the most part, but I'm still > wondering, so here goes: > >>> Unevaluated is meant to pass unevaluated arguments to a function >>> body and as such it works perfectly. No one in practice is interested >>> in (1+1)*Unevaluated[2+2]. > > Do you mean a Function body? If not, Times in that example qualifies > as a function body. (I think.) One uses Unevaluated to prevent a rule from being applied. This means that a rational person will only do it when he knows there is a rule that he does not want to be used. There is no normal situation where one would use Unevaluated and there was no specific evaluation one wanted to prevent. > >>> If now no rules for f can be applied, Mathematica returns the result >>> so far, with Unevaluated wrapped again around the labeled arguments. > > So it's only rules FOR F that matter? Does the distributive property > count as a rule for Times? You do not need Unevaluated to prevent the distributive rule being used because it is never used automatically. You need to apply something like Distribute etc. > >>> If a rule for f can be applied, the administration of arguments >>> that come from Unevaluated is completely skipped. > > I don't get any meaning from the phrase "administration of arguments". I think Fred meant that the rule is applied to the arguments "as given", without changing them or rearranging in any way. > >>> I first formulate my assumption (only WRI and maybe a few others >>> know if I am right!) > > Even if your assumption is correct (as I suspect it is), this > statement doesn't really square with a later claim that there's no > mystery. A certian mystery exists even when we have full documentation, because even that is only a description of expected behaviour of Mathematica and does not include the actual mechanism behind the behaviour (of which at most a vague idea is provided). Everything else requires the source code. If Fred's "speculations" came form an employee of WRI they could have the status of "documentation" without changing a word. The mystery here is simply a question of authoritativeness. Andrzej Kozlowski Chiba, Japan http://www.akikoz.net/~andrzej/ http://www.mimuw.edu.pl/~akoz/

**References**:**Re: Re: Re: Mathematica language issues***From:*"Fred Simons" <f.h.simons@tue.nl>

**Re: Re: Re: Mathematica language issues***From:*DrBob <drbob@bigfoot.com>