Drexel dragonThe Math ForumDonate to the Math Forum



Search All of the Math Forum:

Views expressed in these public forums are not endorsed by Drexel University or The Math Forum.


Math Forum » Discussions » Software » comp.soft-sys.math.mathematica

Topic: What is f[1]? Advanced question
Replies: 9   Last Post: Jul 1, 2013 5:45 AM

Advanced Search

Back to Topic List Back to Topic List Jump to Tree View Jump to Tree View   Messages: [ Previous | Next ]
Noqsi

Posts: 51
Registered: 12/8/10
Re: What is f[1]? Advanced question
Posted: Jun 28, 2013 3:48 AM
  Click to see the message monospaced in plain text Plain Text   Click to reply to this topic Reply

On Thursday, June 27, 2013 4:25:04 AM UTC-6, amannucci wrote:
> Thanks. This is very helpful. I remain puzzled by this:
>
>
>
> u // FullForm
>
> FullForm[Symbol["u"]]
>
> FullForm[Unevaluated[Symbol["u"]]
>
> Head[u]
>
>
>
> FullForm[{1, 2, 3}]
>
> Head[{1, 2, 3}]
>
>
>
> In other words, Head and FullForm seem consist for the list, and inconsistent for the variable u. u's full form is just, literally "u", not Symbol["u"]. But the list's FullForm starts with "List". Head of Symbol["u"] is not Symbol, but "u". What gives?


If FullForm did what you expected, its output would be infinite, because every expression in Mathematica has a head. Remember that the head of an expression is itself an (arbitrary!) expression. So, FullForm "bottoms out" when further expansion would expose an elementary head like Symbol or Integer.




Point your RSS reader here for a feed of the latest messages in this topic.

[Privacy Policy] [Terms of Use]

© Drexel University 1994-2014. All Rights Reserved.
The Math Forum is a research and educational enterprise of the Drexel University School of Education.