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Robert-van-Engelen avatar Robert-van-Engelen commented on May 24, 2024

Good first question! The reason is that list evaluates the arguments 'setq then x and (list '+ x 1)). But this x is the problem, because x is first replaced by n then the n is evaluated by list. A macro constructs code, but the code is still evaluated in a way that may not be immediately intuitive. This is one of the reasons why Lisp implementations have so-called quasiquotes to make this possible, but not easy (ugly) to look at IMHO. Maybe we should add quasiquotes?

EDIT: It's a different problem, it looks like something is not working in setq:

>(define n 1)
>(setq n (+ n 1))
ERR 3 unbound symbol

There is a typo in f_setq that uses 1 instead of *e (environment).

from lisp.

wboeke avatar wboeke commented on May 24, 2024

However ...
This macro works in other lisp 1's. E.g. in tiny-lisp the following is okay:
(setq ++ (macro (x) (list 'setq x (list '+ x 1))))
(setq r 4) (++ r)
Now r equals 5. Quasiquotes not needed, although it would be nice to have them.

from lisp.

Robert-van-Engelen avatar Robert-van-Engelen commented on May 24, 2024

Should work now after the setq typo fix, see my EDIT.

from lisp.

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