What is the difference between a variable and a symbol in LISP?

Question

In terms of scope? Actual implementation in memory? The syntax? For eg, if (let a 1) Is \'a\' a variable or a symbol?

Answer 1

Symbol and variable are 2 different things. Like in mathematic symbol is a value. And variable have the same meaning than in mathematic.

But your confusion came from the fact that symbol are the meta representation of a variable.

That is if you do

(setq a 42)

You just define a variable a. Incidentally the way common lisp store it is throw the structure of a symbol.

In common lips symbol is a structure withe different property. Each one can be access with function like symbol-name, symbol-function...

In the case of variable you can access his value via ssymbol-value

? (symbol-value 'a)
42

This is not the common case of getting the value of a.

? a
42

Note that symbols are self evaluating that mean that if you ask a symbol you get the symbol not the symbol-value

? 'a
A