Re: (byte-compile '(append '(1 2) '(3 4)))

[Basil L. Contovounesios]

Philip Kaludercic [2024-03-16 12:46 +0000] wrote:

> I am not sure what the danger is in the case of constant, quoted lists,
> but I am not familiar with the byte compiler either.  It seems like this
>
> diff --git a/lisp/emacs-lisp/byte-opt.el b/lisp/emacs-lisp/byte-opt.el
> index f75be3f71ad..e6f18590705 100644
> --- a/lisp/emacs-lisp/byte-opt.el
> +++ b/lisp/emacs-lisp/byte-opt.el
> @@ -1599,6 +1599,12 @@ byte-optimize-append
>                           (cdr args))
>                     (cdr newargs)))
>  
> +            ;; (append '(C1...) ... '(C2...)) -> (append C1... ... C2...)
> +            ((cl-loop for arg in args
> +                      always (and (eq (car arg) 'quote)
> +                                  (proper-list-p (cdr arg))))
> +             `',(mapcan #'cadr args))
> +
>              ;; non-terminal arg
>              ((cdr args)
>               (cond
>
>
> would do the trick, and the byte-code is even better:
>
> byte code:
>   args: nil
> 0     constant  (1 2 3 4)
> 1     return    

Is this correct?  According to its docstring, append's last argument
must be eq to the tail of its return value.

-- 
Basil