Re: printing.el again

[Vinicius Jose Latorre <viniciusjl@ig.com.br>]

 > > Ok, but a very long time ago there was a recommendation to do not 
use cl
 > > package when writing code in Emacs Lisp.
 > > Is that recommendation no more valid?
 >
 > CL functions should indeed not be used by packages distributed with 
Emacs.
 > OTOH, CL macros (such as `push', `flet', ...) can be used just fine (just
 > don't forget to put a (eval-when-compile (require 'cl)) at the top of 
your
 > file).

Ok.


 > > > BTW, if you use (featurep 'xemacs) for the test, Emacs-21 will 
optimize
 > > > the test away (since the resulting elc file can't be run on XEmacs
 > > > anyway).  Here it doesn't really matter, but it is sometimes very 
handy
 > > > since it ends up getting rid of spurious warnings about
 > > > XEmacs-specific code.
 > >
 > > Well, so:
 > >
 > > A) (cond ((eq ps-print-emacs-type 'xemacs) ...)
 > >          (t ...))
 > >
 > > B) (cond ((featurep 'xemacs) ...)
 > >          (t ...))
 > >
 > > Are you saying that A and B above are treated differently by the
 > > byte-compiler??
 >
 > Yes.
 >
 > The byte-compiler will not optimize away the `eq' test because it 
considers
 > that the user might change ps-print-emacs-type at any time.  OTOH the
 > byte-compiler knows that since the code it generates doesn't work under
 > XEmacs, (featurep 'xemacs) will always return nil.

So, I'll modify to use (featurep 'xemacs).

Does the byte-compiler do constant folding optimization or it is an ad hoc
optimization?

Maybe this should be documented in Emacs Lisp Reference or in other suitable
info, probably Byte Compiler Users Guide.  Also other byte-compiler
optimizations should be documented.


Vinicius