Why isn't there an `unquote` Lisp primitive?

Question

Lately, I\'ve been thinking a lot about the basis of Lisp; I\'ve read several manuals and/or other materials on the Internet, including The Roots of Lisp by P. ‎Graham:

Answer 1

I am also relatively new to Lisp, but I think that what you were thinking about is eval. evalis the way to change data back to code.

Namely, consider a simple function.

(defun foo (a b c) (list a b c))

Then, if you do something like this, you get a list of symbols:

CL-USER> (foo 'a 'b 'c)
(A B C)

If you add a quote in the front, the function call itself is treated as a piece of data (list):

CL-USER> '(foo 'a 'b 'c)
(FOO 'A 'B 'C)

Adding one more quote has an expected effect:

CL-USER> ''(foo 'a 'b 'c)
'(FOO 'A 'B 'C)

Let us now unwind it with eval, which in essence may be thought of as the inverse operation for the quote. It is the inverse. The x-axis is the data form. The y-axis is the code form. Hopefully this (somewhat stretched) analogy makes sense.

CL-USER> (eval ''(foo 'a 'b 'c))
(FOO 'A 'B 'C)

Can you guess what will happen if I chain two evals in a row? Here it is:

CL-USER> (eval (eval ''(foo 'a 'b 'c)))
(A B C)