I found a Similar question.
But I don't quite understand that explanation.
So I'm trying to run clisp with the following example:
[1]> (defvar a 5)
A
[2]> (+ a 1)
6
[3]> (defparameter b 5)
B
[4]> (+ b 1)
6
[5]> (setf c 5)
5
[6]> (+ c 1)
6
[7]> (setq d 5)
5
[8]> (+ d 1)
6
[9]> (let ((a 500)) (+ a 1))
501
[10]> (let ((b 500)) (+ b 1))
501
[11]> (let ((c 500)) (+ c 1))
501
[12]> (let ((d 500)) (+ d 1))
501
[13]>
What I found is totally the same.
I can't figure out what's different with them?
DEFPARAMETER always assigns a value. So:
[1]> (defparameter a 1)
A
[2]> (defparameter a 2)
A
[3]> a
2
while DEFVAR does it only once, so:
[4]> (defvar b 1)
B
[5]> (defvar b 2)
B
[6]> b
1
SETF is a macro which uses SETQ internally, but has more possibilities. In a way it's a more general assignment operator. E.g. with SETF you can do:
[19]> (defparameter c (list 1 2 3))
[21]> (setf (car c) 42)
42
[22]> c
(42 2 3)
but you can't do that with SETQ:
[23]> (setq (car c) 42)
*** - SETQ: (CAR C) is not a symbol
The following restarts are available:
USE-VALUE :R1 Input a value to be used instead.
ABORT :R2 Abort main loop
Break 1 [24]> abort