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Abstract: I have noticed something really tricky with Mathematica and the documentation for symbols is short on clearing the confusion. It likely reveals what symbols are but it's not very prominent. I know unique symbols are created inside Modules but are they also generated every time we define regular functions and variables?

About The Code: I did a simple test with abc = 123. The output for ?abc gives a grayed out Symbol and SymbolName produces an error message. Does this mean it is not a symbol?

abc = 123
?abc
SymbolName[abc]

Four Questions:

  1. Are system functions symbols?
  2. Are user defined functions symbols?
  3. Are user defined variables symbols?
  4. What are symbols and are they automatically generated?
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1 Answer 1

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Towards your abc example which seems to be the source of confusion: At all times after evaluating abc = 123, abc is a symbol (with full name probably Global`abc, but that depends on the Context[] in which you evaluate it). The problem with SymbolName[abc] is that abc evaluates immediately to 123. The latter is not a symbol, hence SymbolName[123] throws an error. One can obtain the behavior that you probably expected as follows:

SymbolName[Unevaluated[abc]]

"abc"

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    $\begingroup$ Addendum: if you want to use that construct as a pure function, do it this way: ff = Function[Null, SymbolName[Unevaluated[#]], {HoldFirst}]; ff[abc]. $\endgroup$
    – J. M.'s eventual burnout ♦
    May 31, 2020 at 12:45
  • $\begingroup$ @J.M. could it be used in this form as well: ff@abc? Does this form omit the need to set attributes to HoldFirst when used in other contexts like Blocks or user defined functions? Question on the immediate assignment ff = . Shouldn't it be delayed assignment ff := ? $\endgroup$
    – Jules Manson
    Jun 1, 2020 at 5:34
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    $\begingroup$ @Jules: 1. yes; the attributes are already associated with the pure function ff. 2. := would force repeated evaluation of the RHS, so that isn't what you want in that situation; = is the correct choice here. $\endgroup$
    – J. M.'s eventual burnout ♦
    Jun 1, 2020 at 5:37

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