Subject: Variable Capturing and other problems in assoc.el

From: Michael Heerdegen <[email-masked]>
Date: Fri, 22 Jan 2010 18:53:01 +0100

Hello,

In the code of assoc.el, local variables in the functions `aput',
`adelete' and `amake' may hide the alist-symbol in the `eval'-clauses,
which produces wrong results.

Example:
(tested with my Emacs 22 -Q, and also with the current CVS version of
assoc.el):

ELISP> (require 'assoc)
assoc

ELISP> (setq alist '(("a" . 1) ("b" . 2)))
(("a" . 1)
 ("b" . 2))

ELISP> (setq blist '(("a" . 1) ("b" . 2)))
(("a" . 1)
 ("b" . 2))

ELISP> (aput 'alist "a" 123456)
(("a" . 123456))

ELISP> (aput 'blist "a" 123456)
("a" . 123456)

ELISP> alist
(("a" . 1)
 ("b" . 2))

ELISP> blist
(("a" . 123456)
 ("b" . 2))

------

ELISP> (setq alist '(("a" . 1) ("b" . 2)))
(("a" . 1)
 ("b" . 2))

ELISP> (setq blist '(("a" . 1) ("b" . 2)))
(("a" . 1)
 ("b" . 2))

ELISP> (adelete 'alist "a")
(("b" . 2))

ELISP> (adelete 'blist "a")
(("b" . 2))

ELISP> alist
(("a" . 1)
 ("b" . 2))

ELISP> blist
(("b" . 2))

---

Another thing: the doc of `aelement' is misleading in my opinion:

  aelement is a compiled Lisp function in `assoc.el'.
  (aelement KEY VALUE)

  Makes a list of a cons cell containing car of KEY and cdr of VALUE.
  The returned list is suitable as an element of an alist.

The returned value is an one element list with a cons cell, suitable
for `nconc', but not directly as an element of an alist.

---

It is also not fine that `amake' doesn't assign to unbound symbols:

ELISP> (amake 'clist '("a" "b") '(1 2))
*** Eval error ***  Symbol's value as variable is void: clist

so the package misses a real alist constructor.