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From: Kaz Kylheku <643-408-1753@kylheku.com>
Newsgroups: comp.lang.lisp
Subject: Re: lisp-sound v0.2.1
Date: Mon, 17 Feb 2025 16:46:53 -0000 (UTC)
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On 2025-02-17, zara <johan@freecol.be> wrote:
> Every time you do make-dictionary it updates its local *dict. You do not

Every trime you call make-dictionary it redefines a bunch of defuns
that are contained in the function. Their bodies are lambdas, which
capture the current lexical dict* variable, but the functions are global.
Every make-dictionary call you have ever made now uses those new
functions, which refer to the latest dict* variable and not their
original one!

Effectively, your code:

- wipes the dictionary every time the make-dictionary constructor is called.

- has all lambdas returned by make-dictionary working with the same
  dictionary object.

This is the last post in which I'm going to explain it, or reply to
this topic.

>> You are not correct, therefore if you "know" you are correct, there is
>> something wrong with how you determine when you know something
>> and when you don't.
>
> See the clisp output.

What CLISP output? Your only two "test cases" are commented out
by a semicolon?

Here is a real CLISP interaction with your code:

[1]> (defun make-dictionary ()
        (let ((*dict ()))

        (defun add (value)
                (setq *dict (append *dict (list (length *dict) value))))

        (defun get-with-index (index)
                (let ((*index 0))
                        (loop for el in *dict
                                do (if (= (car el) index)
                                        (return (cadr el))
                                (setq *index (+ 1 *index)))
                (return ()))))

        (defun dispatch (msg)
                (cond ((eq msg 'add) #'add)
                        ((eq msg 'get-with-index) #'get-with-index)
                        (T (print "make-dictionary : Message not understood"))))

        #'dispatch))
MAKE-DICTIONARY
[2]> (defvar d0 (make-dictionary))
D0
[3]> (funcall (funcall d0 'add) 'apple)
(0 APPLE)
[4]> (funcall (funcall d0 'add) 'banana)
(0 APPLE 2 BANANA)
[5]> (funcall (funcall d0 'add) 'orange)
(0 APPLE 2 BANANA 4 ORANGE)
[6]> (defvar d1 (make-dictionary)) ;; make new dict, continue with d0
D1
[7]> (funcall (funcall d0 'add) 'peach)
(0 PEACH)

Oops!

Do you see how dictionary d0 has suddenly developed amnesia?

What happened to apple, banana and orange?

Do you think that a dictionary abstration should lose its data
when someone creates another instance? And if that's the design, why
use all these function objects. Why allocate several new lambdas
in each make-dictionary call, when there is only one dictionary?
Just define a global variable:

  (defvar *dict* ())   ;; the one and only dict

  (defun dict-add (index) ...) ;; add to dictionary

Maybe read some books/tutorials. (Try not to close them when you think
you know something different).

-- 
TXR Programming Language: http://nongnu.org/txr
Cygnal: Cygwin Native Application Library: http://kylheku.com/cygnal
Mastodon: @Kazinator@mstdn.ca