bug#49278: 28.0.50; Lisp Mode is for Common Lisp

[Eli Zaretskii <eliz@gnu.org>]

> From: Stefan Monnier <monnier@iro.umontreal.ca>
> Cc: Eli Zaretskii <eliz@gnu.org>,  49278@debbugs.gnu.org
> Date: Tue, 29 Jun 2021 18:59:29 -0400
> 
> Same difference.  It only works for Maclisp to the extent that Maclisp
> is similar to Common Lisp and not because `lisp-mode` is a major mode
> for both Common Lisp and Maclisp.
> 
> > So I reckon lisp-mode wouldn't to a terrible job in most MacLisp
> > programs.  And maybe even SLY and a modern Common Lisp compiler could
> > probably grok MacLisp or Franz Lisp code given sufficient
> > hand-holding.
> 
> IIRC they'd be surprised by the way arrays are treated:
> 
>     http://www.maclisp.info/pitmanual/array.html
> 
> or "hunks":
> 
>     http://www.maclisp.info/pitmanual/hunks.html
> 
> Also `lisp-mode` will happily misfontify and misindent `caseq` and `selectq`:
> 
>     http://www.maclisp.info/pitmanual/contro.html#CASEQ
> 
> [ There are significant incompatibilities, of course.  ]
> 
> The fact that such errors in the handling of Maclisp have not been
> addressed in `lisp-mode` in all these years (despite that Maclisp has
> been a very stable target during those years) shows clearly that
> `lisp-mode` does not try to be a major mode for Maclisp.

We could say something about that to lower user expectations.