Re: new flag? wml -U

[Denis Barbier <nospam@thanx>]

On Mon, Aug 27, 2001 at 02:36:30PM +0200, Jan Holler wrote:
> Hi Denis
> 
> On 27-Aug-01 Denis Barbier wrote:
> > On Thu, Aug 16, 2001 at 04:18:44PM +0200, Jan Holler wrote:
> >> 
> >> I suggest to implement a flag -U to undefine previously with
> >> -D defined variables.
> 
> >> <if <var-exists BAR>
> >> <set-var newbar=<get-var bar>>           # or $(BAR) instead of <get-var bar>
> >> <set-var newbar=$(WML_SRC_BASENAME)>
> >> >
> 
> > problem is that wml has then to distinguish between
> >   -D foo=bar -U foo
> > and
> >   -U foo -D foo=bar
> > which is not trivial.
> 
> Regard the order: last flag wins over earlier flags from the 
> left to the right (.wmlc -> top down). Would that still be 
> complicated to implement in the "command-line"-parsing?
> 
> > IMO it is always possible to unset a variable by making it empty,
> > and replace your test by <if <get-var BAR> ...
> 
> Thanks. That would work around. But needs some
> extra effort (need to unset it in every file or make
> global changes in some include-file) and is IMHO not 
> that flexible as the described '-U'. (speaking of
> global and hierarchical settings).

Agree, but there is indeed a problem, all flags are handled separatly.
This is quite common, I do not know any command-line parser which takes
care of flags' order, and the Perl module Getopt::Long do not derogate
to this rule.
So, we would have to parse command-line and .wmlrc twice, first time
with Getopt::Long, then with a single regex checker to determine -D/-U
order.  I would prefer avoiding this solution.

Maybe we could adopt a convention, say -Dfoo=_undef to ask wml to
undefine this value (and also delete all previous declarations) before
passing it to every pass, a patch is attached, you may apply it against
wml_frontend/wml.src or your wml script.

-- 
Denis Barbier
WML Maintainer
Index: wml.src
===================================================================
RCS file: /home/barbier/Projets/Wml/cvs/wml/wml_frontend/wml.src,v
retrieving revision 1.74
diff -u -u -r1.74 wml.src
--- wml.src	2001/08/26 00:43:41	1.74
+++ wml.src	2001/08/27 13:28:42
@@ -543,6 +543,17 @@
     push(@opt_o,$opts);
 }
 
+#   7. Undefine variables when requested
+%new_opt_D = ();
+foreach $d (@opt_D) {
+    ($var, $val) = ($d =~ m|^(.+?)=(.*)$|);
+    if ($val eq '_undef') {
+        delete $new_opt_D{$var};
+    } else {
+        $new_opt_D{$var} = $val;
+    }
+}
+@opt_D = map { $_."=".$new_opt_D{$_} } keys %new_opt_D;
 
 #   fix the verbose level
 if ($opt_v == 0) {