(add-to-list 'll "a")
(delete-dups ll)

The variable "ll" needs be quoted in add-to-list, while not quoted in
delete-dups, why? any special reasons?

sunway gmail.com> writes:

Lisp passes its arguments by-value.

Therefore a function cannot modify the variables from which the values
it gets come.

It still can modify the value, when it is mutable, but not the variable.

Usually, when we want to have a variable (or in general, a place)
modified, we have to use a macro, or a special operator.

(setq ll (list 1 2 3)) ; setq is a special operator.
(require 'cl)
(push 0 ll) ; push is a macro

Otherwise, you must take care to get the result and store it back into
the variable:

push is indeed a macro, but there's no need to require 'cl anymore,
push is now available in Emacs Lisp.

"elisp lacks of lexical variable", if this happens to the C
programming language:
int a=10;
foo(a);
may be "a" will be changed to 9 ?

if so, I really hate this feature....

On Sep 13, 5:38 pm, p...@informatimago.com (Pascal J. Bourguignon)
wrote:

sunway gmail.com> writes:

1- not in C, but in C++ you can have:
void foo(int& v){ v=0; }
void f(){
int a=10;
foo(a);
assert(a==0);
}