Noqsi
Posts:
51
Registered:
12/8/10


Re: What is f[1]? Advanced question
Posted:
Jun 28, 2013 3:48 AM


On Thursday, June 27, 2013 4:25:04 AM UTC6, 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.

