GNU bug report logs - #47302
27.1; calc math-format-number formatting for floats without decimals is unusual

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From: Mattias Engdegård <mattiase <at> acm.org>
To: Dave Gillespie <Daveg <at> synaptics.com>
Cc: Jelle Licht <jlicht <at> fsfe.org>, Stefan Kangas <stefan <at> marxist.se>, "47302 <at> debbugs.gnu.org" <47302 <at> debbugs.gnu.org>
Subject: bug#47302: 27.1; calc math-format-number formatting for floats without decimals is unusual
Date: Sun, 25 Apr 2021 17:53:30 +0200

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22 apr. 2021 kl. 18.35 skrev Dave Gillespie <Daveg <at> synaptics.com>:

> Wow, it has been a long time since I got any correspondence on Calc!

Good to hear from you, Dave! I just fix the occasional Calc bug now and then.

> Calc has a C language mode ('d C' keystroke, controlled by calc-language).  It is a good point that C mode (and probably others like it) should format integer-valued floats as "123.0" even if the default mode does not.  If we apply Jelle's patch, I suggest making it conditional on calc-language so that it applies only in modes such as C mode.  Or perhaps rework it as a text transformation using calc-language-filter.
> 
> You could even create a JSON language mode, but most likely the basic C mode is close enough to serve that purpose.

These are all good suggestions. Most languages permit trailing decimal points; the only common exceptions that I can think of are Haskell, Ada and Swift. Apparently JSON is also one. Tying the float-format display to the C, Pascal (etc) modes seems a bit incongruous as it has nothing to do with the syntax of those languages.

How to display a floating-point number with zero fraction also depends on what the user wants to do with the result, so there is a good argument for letting him or her do the required post-processing. Sometimes '1.' should become '1.0', sometimes '1'. For instance, in a LaTeX document it would depend on how the author wants to represent significant digits. A JSON parser (such as the one in Emacs) will parse '1.0' and '1' differently, as a float or integer respectively.

I wrote the patch below as a possible solution but in the light of the above, perhaps it's not ideal?

[calc-digit-after-point.diff (application/octet-stream, attachment)]

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