On Fri, 09 May 2008, frank van nuffel wrote:
Hi Frank,
> the #define is on _EXPAND_() not on _EXPAND_, so #undef _EXPAND_
> won't be substituted, but at the same time it #undef's _EXPAND_()
Yes, you are right. I missed. Sorry I should more carefully check
your example.
> >It's for Harbour only. If you want to adopt it to Clipper then you have
> >to make the trick with #include I've written above: create file undef.ch
> >with one line:
> > #undef _EXPAND_
> >and in the above code change:
> > #undef _EXPAND_
> >to:
> > #include "undef.ch"
> >Such tricks makes also class(y).ch
> i'm aware of such construct, but it isn't necessary here (see above)
Not exactly. There are situations when using indirect #include resolves
some problems which cannot be easu addressed using Clipper's PP.
I updated your example to work with Clipper and Harbour and to not use
overloaded #[x]trans rules.
/* --- system definitions ----- */
#xCOMM MACRO SECTION BEGIN => #undef _EXPAND_
#xCOMM MACRO <f>( [ <a,...> ] ) <b> => #define <f>( <a> ) ;
ANY_DEF( ppparam, ( _SUSPAND_() <f> | <b>, <a> ) _EXPAND_() )
#xCOMM MACRO SECTION END => #define _EXPAND_()
#xCOMM MACRO SUSPEND => #undef _SUSPAND_
#xCOMM MACRO RESUME => #define _SUSPAND_()
#define _REPEAT_()
#define ANY_DEF( x, y ) ANY_TRANS( x, y )
#xTRAN ANY_TRANS( <x>, ( [<s:_SUSPAND_()>] <y,...> ) ) => ;
<x>( _REPEAT_() <s> <y> )
#xTRAN ppparam( <f> | <b> [, <a,...>] ) => <b>
#xTRAN ppparam( _SUSPAND_() <f> | <b> [, <a,...>] ) => <f>( <a>, )
# TRAN function ppparam( [_SUSPAND_()] <f> | <b> [, <a,...>] ) => ;
func <f> ; PARAM <a>
# TRAN procedure ppparam( [_SUSPAND_()] <f> | <b> [, <a,...>] ) => ;
func <f> ; PARAM <a>
/* --- end of system definitions ----- */
Please look that if you want to use _SUSPAND_() define then it's
necessary to force switching translation to defines. ANY_DEF() does it.
Unlike the previous one current Harbour's PP uses the same algorithm
for rule parsing as Clipper so it's necessary also in Harbour.
In this test instead of '%%' you were usinf I used _REPEAT_() define.
It makes exactly the same job in changing substitution precedence as
%% in your examples though it also forces parsing DEFINEs. If you do
not want to parse define (in this example is not necessary) then you
can change #define _REPEAT_() to #xtrans _REPEAT_() =>
I hope it may help you to understand the exact substitution precedence
used by PP which is different then described in Clipper documentation.
In fact it looks like:
1. substitute _ALL_ DEFINEs
2. if anything was substituted in last pass goto 1
3. substitute _ALL_ #[x]TRANs
4. if anything was substituted in last pass goto 3
5. if anyhthing was substituted in any of #[x]TRANs passes goto 1
6. substitute _ALL_ #[x]COMMANDs
7. if anything was substituted in last pass goto 6
8. if anyhthing was substituted in any of #[x]COMMANDs passes goto 1
> >If you need general solution then we should introduce new PP token
> >which is significant for PP but neutral for compiler. F.e. <->
> >as result marker.
> > #trans func( <a,...> ) => func( <-> 1, <a> )
> >The <-> in result pattern will block infinite translation and because
> >it will be invisible for compiler then it will not break compilation
> >process. I can add such marker in the future.
> And you did! That would be welcome, i vote for!
Probably we should discuss it. I think it will be good to also have
named invisible markers which can be used in other rules. I hope that
after 1.0 we can return to this discussion.
best regards,
Przemek
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