Re: Lisp reader syntax and bootstrap

[Paul Eggert]

On 2023-07-12 21:27, Po Lu wrote:
> Lisp programmers should simply avoid using NaN and Inf

Support for NaN and Inf is ubiquitous nowadays, and it should be OK to 
write Emacs Lisp programs that use NaN and Inf, especially since Emacs 
itself uses them in its own Lisp files.

As I actually made money back in the 1970s writing code for VAXes, I was 
moved to look into RMS's suggestion to signal an error when reading 
"0.0e+NaN" on a VAX. Unfortunately this broke calculator.el - that is, I 
couldn't load calculator.el (or calculator.elc), as loading signaled an 
error when it saw the NaN. And even if we removed the NaN from 
calculator.el (and I suppose, infinities from other .el files), users 
would run into similar issues with their own code.

So I instead installed the attached patch. On a VAX this approximates 
infinities and NaNs with extremal values and non-numeric objects, 
respectively. Although I do not have a VAX to test it on, and am too 
lazy to spin up an emulator, I did test it on x86-64 by pretending that 
the x86-64 lacked IEEE support, and it seemed to work OK. (At least, I 
could load calculator.el....)

This patch shouldn't change behavior (or even the executable code) on 
today's platforms. It's purely for computer museums.

0001-Port-NaN-infinity-handling-better-to-VAX.patch
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