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Re: What does FullForm[ ] actually do?

  • To: mathgroup at smc.vnet.net
  • Subject: [mg90710] Re: What does FullForm[ ] actually do?
  • From: Bill Rowe <readnews at sbcglobal.net>
  • Date: Sun, 20 Jul 2008 06:34:17 -0400 (EDT)

On 7/19/08 at 4:49 AM, siegman at stanford.edu (AES) wrote:

>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.

Given all of the built-in queries (at least that I know about)
end in "Q", it is clear neither of these were intended as queries.

>You invoke them to ask, what "What will some expr do?", not to say
>"Do this and tell me what you did".

Neither FullForm nor Options tell you what some expression will
do nor what some expression did. FullForm tells you the form of
the evaluated expression. Not what it did, nor what it will do.

>This seems even more obvious for Options[] than for FullForm[] -- yet
>Options evaluates also.

I don't at all understand why this would be an issue. Options
provides a list of the options set for a specific object. That
is when you do

Options[Integrate]

you get a list of each of the options for Integrate and their
current setting. Using Integrate as an example, the only way I
can see evaluation being an issue is if you did something like

Options[Integrate[x,x]]

Why would anyone want to do this instead of Options[Integrate]?

>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.

Think about what you are asking here. How is any Mathematica
function to determine what the result would be if an expression
were evaluated without evaluating that expression? Keep in mind
an expression can be any compound expression which can include
results of external programs. And even if an expression is
limited to built-in functions, the result can be literally
anything that can be put on your hard drive or displayed on the screen.


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