An argument can be a symbol that returns a value when it is evaluated.
For example, when the symbol fill-column by itself is evaluated,
it returns a number. This number can be used in an addition. Position
the cursor after the following expression and type C-x C-e:
(+ 2 fill-column)
The value will be a number two more than what you get by evaluating
fill-column alone. For me, this is 74, because the value of
fill-column is 72.
As we have just seen, an argument can be a symbol that returns a value
when evaluated. In addition, an argument can be a list that returns a
value when it is evaluated. For example, in the following expression,
the arguments to the function concat are the strings
"The " and " red foxes." and the list (+ 2
fill-column).
(concat "The " (+ 2 fill-column) " red foxes.")
If you evaluate this expression, "The 74 red foxes." will
appear in the echo area. (Note that you must put spaces after the
word `The' and before the word `red' so they will appear in
the final string.)
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