Question

(message "%s" 'abc)
(message "%s" "abc")

I found that both the former expression will be the same result( in emacs ).
Although I know this is not really a property example to show my question.

Could you explain more about what’s the exact meaning for a quoted symbol?
And the what does the quoted symbol return? A string representation of a variable name or something else?

Answer 1

Symbols in Lisp can serve several purposes, including, but not limited to:

• a simple data type for representing anything atomic that the other simple data types cannot or should not — thus similar to enumerations in C-family languages. For instance, a function MakeWidget may take an argument Size, the possible values of which are ‘small, ‘medium, and ‘large. Symbols used this way need not be declared, though there are simple means to limit the range of values if need be.
• variable name
• function name

A quoted symbol returns the symbol itself.

A symbol can be printed, and, as as you saw, prints just like a string.

So, why would you want to use a symbol when you can just as easily use a string?

• the name of a symbol doesn’t change, so it uses less memory than a string
• a symbol can be used to store a reference to a function you want to call in a non-trivial way. A typical example is applying a function to a list — e.g., if square is a properly defined function, then:

(apply #'square '(1 2 3 4))

returns

(1 4 9 16)

There are other uses for symbols not mentioned here, but hopefully this gives you a good start.