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Re: What is f[1]? Advanced question

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  • Subject: [mg131322] Re: What is f[1]? Advanced question
  • From: David Bailey <dave at>
  • Date: Fri, 28 Jun 2013 04:13:33 -0400 (EDT)
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  • References: <> <kqdshl$n34$> <kqh3u0$2im$>

On 27/06/2013 11:25, 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?
I don't think there is too much mystery here - FullForm would simply be 
too clumsy if it expanded symbols into Symbol constructs. As it is, 
FullForm is incredibly useful.

I wish there was also a variant that did not evaluate its argument. True 
one can write:

expression //Hold//FullForm

but the expression gets contaminated with Hold.

David Bailey

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