Re: Define progn_ignore to run Fprogn and ignore output

[Alan Mackenzie]

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).