the list inside a list of lisp tutorial

问题

I am reading Programming in Emacs Lisp

Here is another list, this time with a list inside of it:

     '(this list has (a list inside of it))

I am confused with the nested list, why it has not a prefix quoting as

 '(this list has  '(a list inside of it))

if not has a prefix `, why it not parse the a as a function?

回答1:

's-expression is an abbreviation for (quote s-expression): anything inside the s-expression is considered a datum and it is not evaluated.

So,

'(this list has (a list inside of it))

is an abbreviation of:

(quote (this list has (a list inside of it)))

that contains the following list:

(this list has (a list inside of it))

which is the value of the entire quote form since it is not evaluated.

It is easy to verify this by writing:

'(this list has '(a list inside of it))

This, if evaluated, will produce as value the following list:

(this list has (quote (a list inside of it)))

回答2:

That's one of the slight difficulties in Lisp: a list is data and can also be a program. If you want a list to be data in a Lisp program, you need to quote it.

Lists as such: one can read them with READ

(this list has (a list inside of it))
(this list has no list inside of it)
(+ 1 2)
(1 2 +)
(1 + 2)
(quote (this list has (a list inside of it)))
(quote (this list has (quote (a quote list inside of it))))
(quote quote)

Valid Lisp forms: one can evaluate them with EVAL

(+ 1 2)
Evaluates to -> 3

(quote (+ 1 2))
Evaluates to -> (+ 1 2)

(quote (this list has (a list inside of it)))
Evaluates to -> (this list has (a list inside of it))

(quote quote)
Evaluates to -> quote

This is also a valid Lisp form:

(quote (this list has (quote (a quoted list inside of it))))

It evaluates to:

(this list has (quote (a quoted list inside of it)))

来源：https://stackoverflow.com/questions/56523328/the-list-inside-a-list-of-lisp-tutorial