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Re: What does FullForm[ ] actually do?

  • To: mathgroup at smc.vnet.net
  • Subject: [mg90685] Re: What does FullForm[ ] actually do?
  • From: AES <siegman at stanford.edu>
  • Date: Sat, 19 Jul 2008 04:49:53 -0400 (EDT)
  • Organization: Stanford University
  • References: <g54oj0$eu9$1@smc.vnet.net> <g56t9n$3qv$1@smc.vnet.net> <g5pivs$qb1$1@smc.vnet.net>

In article <g5pivs$qb1$1 at smc.vnet.net>, magma <maderri2 at gmail.com> 
wrote:

> 
> AES you certainly have a lot of time to split hair and write about
> it :-) Good for you.
>

Point taken, and well put (though I'm not sure whether the final three 
words are to be taken seriously, or sarcastically).  I've been making 
serious resolutions in fact, to spend more of time splitting wood rather 
than hair, or at least doing something else involving physical rather 
than mental exercise.  (My wife strongly agrees.)

But two final points on this topic:

1)  Consider Options[] in addition to FullForm[].  

To my way of thinking, FullForm[] and Options[] are both _queries_ 
-- you use them to get information, in preparation for (maybe) doing 
something, but not to accomplish something.  

You invoke them to ask, what "What will some expr do?", not to say "Do 
this and tell me what you did".  This seems even more obvious for 
Options[] than for FullForm[] -- yet Options evaluates also.

And this seems even more relevant when the evaluation of said expr can 
readily have other totally unrelated effects and impacts that don't show 
up at all in the output of FullForm or Option[], and have nothing to do 
with that output. Try some tests, for example, with expr's of the form 
expr1;expr2;expr3 --  1 and 2 seem to get evaluated along with 3, but 
you only get information about 3.

When I ask my banker, WhatsTheMeaningOf["Balance available for immediate 
withdrawal"], that does NOT mean "Withdraw that balance and tell me what 
it is".

2)  Couldn't there be an alternative and more reasonable choice for the 
operation of FullForm[expr] besides just evaluate expr or don't -- 
like,"Show me what the full form result would be _IF_ this expr were 
evaluated" -- but don't, for God's sake, evaluate it -- I'll do that 
when I'm ready to.


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