In article <3ff489d3$1@news.povray.org>,
 Florian Brucker <tor### [at] torfboldcom> wrote:

> >   I think this should be explained in the documentation if it's not already.
> IMHO an implementation like the documentation is described would be 
> better that updating the documentation. I think the current behaviour is 
> not at all intuitive and can create errors which are very hard to spot. 
> Although I have to admit that I have never encountered this error before :)

It is also very useful. Look at the Isect() and Extents() macros in 
shapes.inc, which use this feature to return multiple values.
Things could be clarified quite a bit, though. This is what I would do:

#declare always declares a global variable. Actually, deprecate #declare 
and use #global instead. #local always declares a local variable.

If either #declare or #local are used with an existing variable, a 
warning is emitted. Existing variables are modified with a #set or # 
directive, which require an existing variable:

#local J = 0;
#while(J < 10)
    #set J = J + 1;
or
    #J = J + 1;
#end

#macro Foo(Param)
    #local Param = Param + 1;
#end
Would produce a warning and replace the parameter Param with the local 
version, leaving the original unaffected.

#macro Foo(Param)
    #declare Param = Param + 1;
#end
Would only produce a warning if a global variable named Param already 
existed. It would create that global variable and leave the parameter 
unaffected.

#macro Foo(Param)
    #set Param = Param + 1;
#end
Would modify the parameter itself.

This also avoids odd typo errors. This code would loop infinitely:
#local I = 0;
#while(I < 10)
    #local l = I + 1;
#end

This version would give an immediate error:
#local I = 0;
#while(I < 10)
    #set l = I + 1;
#end

The #set keyword is part of the MegaPOV patch collection, but the rest 
of it would break backwards compatibility too much to be included. 
Unless a new keyword were used for declaring local variables...hmm. How 
does this sound?

#declare, #local: obsolete, deprecated, but unchanged in operation for 
backwards compatibility.
#global, #def or #define, #set: as described above, with #def declaring 
a local variable.

Well, I just wanted to say that the pass by reference is actually a 
useful feature...guess I got carried away.


> BTW, any chance the POV-Syntax will be extended with a include-file-wide 
> identifier scope? Something like (In an include file):

This already exists: variables defined as #local outside a macro are 
local to the include file.

-- 
Christopher James Huff <cja### [at] earthlinknet>
http://home.earthlink.net/~cjameshuff/
POV-Ray TAG: <chr### [at] tagpovrayorg>
http://tag.povray.org/

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