What is the difference between 1 and '1 in Lisp?

Question

I had never really thought about whether a symbol could be a number in Lisp, so I played around with it today:

> \'1
1
> (+ \'1 \'1)
2
> (+ \'1 1)
2
>         


        

Answer 1

In Common Lisp, '1 is shorthand for (QUOTE 1). When evaluated, (QUOTE something) returns the something part, unevaluated. However, there is no difference between 1 evaluated and 1 unevaluated.

So there is a difference to the reader: '1 reads as (QUOTE 1) and 1 reads as 1. But there is no difference when evaluted.