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Questions regarding char-table-range RANGE arg

From: Federico Tedin
Subject: Questions regarding char-table-range RANGE arg
Date: Thu, 31 Aug 2023 23:54:01 +0200
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101 Thunderbird/102.13.0

Hi everyone,

I was trying to understand better how char tables work but I got stuck at the following:

In the docs for `char-table-range' (https://www.gnu.org/software/emacs/manual/html_node/elisp/Char_002dTables.html), it is mentioned that it is possible to specify (from . to) as the value for RANGE. This already seemed a bit unexpected for me, as the function is supposed to retrieve a single value from the char table - how could it do it for a range, where potentially many different values
could be defined? I did some tests:

(setq tt (make-char-table nil))

(set-char-table-range tt (cons 10 20) "foo")
(set-char-table-range tt (cons 21 25) "bar")

(char-table-range tt (cons 5 15)) ; includes some "foo" values?
  -> nil ; no

(char-table-range tt (cons 10 15)) ; includes some "foo" values?
  -> "foo" ; yes, makes sense

(char-table-range tt (cons 15 22)) ; includes some "foo" and "bar" values?
  -> "foo" ; ok, only the first range was considered

(char-table-range tt (cons 15 0)) ; what if I set `to' to a nonsensical value?
  -> "foo"

(char-table-range tt (cons 15 99999)) ; or this one
  -> "foo"

(char-table-range tt (cons 26 30)) ; should return nil
  -> nil ; ok

So from my tests it seems like only `from' is considered? Similar to the case where RANGE is just a character. I was hoping someone with a better understanding of character tables could maybe explain the behaviour observed above. It is possible it could me just missinterpreting the documentation (I am trying to keep a more end-user perspective for this, i.e. not look at the Emacs source code and only use documentation). I did try looking also into chartab-tests.el though but could not find more information there.


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