From Newsgroup: gnu.emacs.help

excalamus@tutanota.com writes:

Some questions about alists:
- Is it a better practice to convert string keys to symbols?

I would recommend keeping the data the way it is. Strings are great;
emacs has hash tables that will work well for strings.

-a Is =intern= best for this?-a

No. read-from-string will do better. You don't want numbers and commas
in your symbols.

What about handling illegal symbol names?

the function make-symbol will handle this for you.

- If a symbol is used as a key and that symbol is already in use
-a elsewhere, is there potential for conflict with the existing symbol?

Oh yes. In common lisp the convention for global variables is to use `*'
around the symbol; such as *gensym-counter*. In emacs lisp, it is
considered bad form to use such constraints because it messes up the minibuffer, etc.

I have an alist created from parsing meta data from a file.-a The file
looks like:

#+begin_src emacs-lisp :results verbatim :session exc

[ ... ]

I do not know why you are using the hash `#'?

(defvar exc-post-meta-data
-a (concat
-a-a "#+TITLE: Test post\n"
-a-a "#+AUTHOR: Excalamus\n"
-a-a "#+DATE: 2020-07-17\n"
-a-a "#+TAGS: blogging tests\n"
-a-a "\n")
-a "Sample post meta information.")

You could do.

(defvar executable-find '((:TITLE . "Test Post") (:AUTHOR . "Name")))

This works, but seems like a smell.-a All these problems go
back to strings as keys.-a Maybe there's a better way?

I could convert the keys to symbols using =intern=.-a

I would try hash tables for strings. see below.

#+RESULTS:
: ((TITLE . "Test post") (AUTHOR . "Excalamus") (DATE . "2020-07-17") (TAGS . "blogging tests"))

This has several apparent problems.

As I understand it, this would pollute the global obarray. Is that a
real concern?-a I know the symbol is only being used as a lookup;

Yes it is.

the variable, function, and properties shouldn't change.-a

This is the key. You seem to understand it. In emacs lisp there are not duplicate symbols. Two symbols are compared by their address (or
pointer) which is called `EQ' meaning that they are the same thing.

if you are re-using symbols; i.e., if the symbols are finite then
using them should not be a problem. Such as in your case; TITLE, AUTHOR,
these are good for symbols. Parsing an email with each word as a symbol
can cause serious problems with the obarray.

However you could intern the symbols into a different obarray.

The biggest difference will be at run time. You have to make a hashtable
at runtime (to be simple about it). With an alist of symbols emacs will
already place the symbols into it's obarray without the extra code.

Regardless, I
don't want my package to conflict with (i.e. overwrite) a person's environment unknowingly.

In common lisp their are namespaces; but the problem is the same.
partitioning code is not my specialty.

The string may also have characters illegal for use as a symbol.-a
Here's what happens with illegal symbol characters in the string.

#+begin_src emacs-lisp :results verbatim :session exc
(setq exc-bad-meta-data
-a (concat
-a-a "#+THE TITLE: Test post\n"
-a-a "#+AUTHOR: Excalamus\n"
-a-a "#+DATE: 2020-07-17\n"
-a-a "#+POST TAGS: blogging tests\n"
-a-a "\n"))

(setq exc-alist-i-bad (exc-parse-org-meta-data-intern exc-bad-meta-data)) exc-alist-i-bad
#+end_src

#+RESULTS:
: ((AUTHOR . "Excalamus") (DATE . "2020-07-17"))

How are situations like these best handled?

I usually use sed, awk, or perl for the input. I write shell script to
create a simple A-LIST or a file with lines of strings.

I wish there was a way to write a hashtable to output.
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