Re: Define progn_ignore to run Fprogn and ignore output

[Chris Gregory <czipperz@gmail.com>]

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Oh yes you are correct. That's my bad.

Sincerely,

Chris Gregory

On Tue, Dec 27, 2016 at 9:49 AM, Alan Mackenzie <acm@muc.de> wrote:

> Hello, Chris.
>
> Just a small point about your proposed patch.
>
> On Mon, Dec 26, 2016 at 08:14:47PM -0600, Chris Gregory wrote:
> > This patch defines progn_ignore to do Fprogn but not return a result.
> > This will minorly speed up all operations using `unwind_body'.  It also
> > simplifies the code for `Fprog1' without sacrificing performance.
>
> > diff --git a/src/eval.c b/src/eval.c
> > index ddcccc2..7e02838 100644
> > --- a/src/eval.c
> > +++ b/src/eval.c
> > @@ -456,10 +456,17 @@ usage: (progn BODY...)  */)
> >  /* Evaluate BODY sequentially, discarding its value.  Suitable for
> >     record_unwind_protect.  */
>
> > +static void
> > +progn_ignore (Lisp_Object body)
> > +{
> > +  while (CONSP (body))
> > +    eval_sub (XCAR (body));
> > +}
> > +
>
> Doesn't the above code up an infinite loop?  `body' appears not to be
> changed between iterations of the while.
>
> >  void
> >  unwind_body (Lisp_Object body)
> >  {
> > -  Fprogn (body);
> > +  progn_ignore (body);
> >  }
>
> >  DEFUN ("prog1", Fprog1, Sprog1, 1, UNEVALLED, 0,
> > @@ -470,15 +477,8 @@ usage: (prog1 FIRST BODY...)  */)
> >    (Lisp_Object args)
> >  {
> >    Lisp_Object val;
> > -  Lisp_Object args_left;
> > -
> > -  args_left = args;
> > -  val = args;
> > -
> > -  val = eval_sub (XCAR (args_left));
> > -  while (CONSP (args_left = XCDR (args_left)))
> > -    eval_sub (XCAR (args_left));
> > -
> > +  val = eval_sub (XCAR (args));
> > +  progn_ignore (XCDR (args));
> >    return val;
> >  }
>
> --
> Alan Mackenzie (Nuremberg, Germany).
>

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