Executing code stored as a list

Question

After understanding (quote), I'm curious as to how one might cause the statement to execute. My first thought was

(defvar x '(+ 2 21))
`(,@x)

but that just evaluates to (+ 2 21), or the contents of x. How would one run code that was placed in a list?

Answer 1

(eval '(+ 2 21))

Answer 2

@Christián Romo:

Backtick example: you can kinda implement apply using eval and backtick, because you can splice arguments into a form. Not going to be the most efficient thing in the world, but:

(eval `(and ,@(loop for x from 1 upto 4 collect `(evenp ,x))))

is equivalent to

(eval '(and (evenp 1) (evenp 2) (evenp 3) (evenp 4)))

Incidentally, this has the same result as the (much more efficient)

(every 'evenp '(1 2 3 4))

Hope that satisfies your curiosity!

Answer 3

Take a look at funny Lisp tutorial at http://lisperati.com/. There are versions for Common Lisp and Emacs Lisp, and it demonstrates use of quasiquote and macros.