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bug#55395: What does (1 2 3 . #2) mean?
From: |
Stefan Monnier |
Subject: |
bug#55395: What does (1 2 3 . #2) mean? |
Date: |
Sat, 14 May 2022 09:45:15 -0400 |
User-agent: |
Gnus/5.13 (Gnus v5.13) Emacs/29.0.50 (gnu/linux) |
>> The main goal is to avoid inf-looping and the #NNN chosen is
>> somewhat arbitrary.
> It seems to have sort-of worked before and was broken, inadvertently and
> with the best intentions, by a later change.
>
> Additionally the #N value appears to be correct for other object types. For
> example,
>
> [a [b #1=[[c #1# d]]]]
>
> is printed as
>
> [a [b [[c #2 d]]]]
>
> which is consistent with the manual.
I do have the impression that it used to be "correct", but I can't
remember of a single time where I actually made use of that NNN.
And even if you know what it means and it works correctly, it's pretty
hard for a normal human to correctly count the depth starting from
the root.
I suspect if we want to "do better", printing "the beginning" of the
object to which we're looping (and saying explicitly that there's
a cycle) will be a lot more useful to the average user.
[ Or we could even print "the period" rather than "the beginning". ]
>> I'm personally more bothered by the fact that those #NNN use exactly the
>> same syntax as used with `print-circle` yet they don't have the
>> same semantics.
> The syntax isn't exactly the same (#N vs #N= and #N#) but annoyingly close.
Indeed, it's not as bad as I remembered.
> For that matter I would have preferred numbering the other way, starting at
> the bottom going up, like de Bruijn indices.
I love&hate de Bruijn indices as much as the next guy, but they're not
human-friendly (even more than the "like de Bruijn levels" we currently
use).
Stefan
- bug#55395: What does (1 2 3 . #2) mean?, Mattias Engdegård, 2022/05/13
- bug#55395: What does (1 2 3 . #2) mean?, Lars Ingebrigtsen, 2022/05/13
- bug#55395: What does (1 2 3 . #2) mean?, Stefan Monnier, 2022/05/13
- bug#55395: What does (1 2 3 . #2) mean?, Lars Ingebrigtsen, 2022/05/13
- bug#55395: What does (1 2 3 . #2) mean?, Mattias Engdegård, 2022/05/13
- bug#55395: What does (1 2 3 . #2) mean?,
Stefan Monnier <=
- bug#55395: What does (1 2 3 . #2) mean?, Mattias Engdegård, 2022/05/18
- bug#55395: What does (1 2 3 . #2) mean?, Stefan Monnier, 2022/05/18
- bug#55395: What does (1 2 3 . #2) mean?, Mattias Engdegård, 2022/05/23
bug#55395: What does (1 2 3 . #2) mean?, Andreas Schwab, 2022/05/13