Re: GNU Emacs raison d'etre

[Dmitry Gutov]

On 21.05.2020 05:28, Eli Zaretskii wrote:
> > > eval-last-sexp uses prin1 to display the result, so it is not
> > > affected, as intended.
> > But aren't all echo area displays targeted at the user anyway?
> >
> > I'm not saying the current behavior is necessarily "broken", but perhaps
> > we could enhance it further.
> The intent was to affect messages that are a "surprise" for the user.
> eval-last-sexp is invoked by the user, so no surprise here.

But not all 'message' calls are a "surprise". One might even say that 
the vast majority of them aren't. And yet, they obey set-message-function.

eval-last-sexp uses 'prin1' under the covers. While it's different from 
'message', it's not entirely clear to me that it's intended to be 
different semantically, e.g. used for distinctly different purposes. So 
I might as well imagine the same code that calls 'message' decide at 
some point to call 'prin1' (in addition to 'message', or instead).

Looking at its description, it could delegate to 'standard-output', 
which is overridable. It's not particularly convenient, though.

But this patch would do it:

@@ -1132,7 +1132,7 @@
     ;; Setup the lexical environment if lexical-binding is enabled.
     (elisp--eval-last-sexp-print-value
      (eval (eval-sexp-add-defvars (elisp--preceding-sexp)) 
lexical-binding)
-     (if insert-value (current-buffer) t) no-truncate char-print-limit)))
+     (if insert-value (current-buffer)) no-truncate char-print-limit)))

 (defun elisp--eval-last-sexp-print-value
     (value output &optional no-truncate char-print-limit)