Nested [IFDEF]s not working?

[Andreas Färber]

Hello,

A construct like:

[IFDEF] CONFIG_PPC
   [IFDEF] CONFIG_PPC64
     5
   [ELSE]
     4
   [THEN]
[ELSE]
   [IFDEF] CONFIG_SPARC64
     6
   [ELSE]
     3
   [THEN]
[THEN]

has been seen to return, e.g., 4 3 according to the debug word.

Is this nesting forbidden in Forth? Easily fixable? A better way to do  
this? I do want a final catch-all since returning no value would have  
unexpected results, and we currently do not have a define CONFIG_PPC32  
so that a concatenation of independent [IFDEF]...[THEN]s wouldn't work.

TIA,

Andreas

[Mark Cave-Ayland]

Andreas Färber wrote:
> Hello,
>
> A construct like:
>
> [IFDEF] CONFIG_PPC
>   [IFDEF] CONFIG_PPC64
>     5
>   [ELSE]
>     4
>   [THEN]
> [ELSE]
>   [IFDEF] CONFIG_SPARC64
>     6
>   [ELSE]
>     3
>   [THEN]
> [THEN]
>
> has been seen to return, e.g., 4 3 according to the debug word.
>
> Is this nesting forbidden in Forth? Easily fixable? A better way to do 
> this? I do want a final catch-all since returning no value would have 
> unexpected results, and we currently do not have a define CONFIG_PPC32 
> so that a concatenation of independent [IFDEF]...[THEN]s wouldn't work.

IIRC [IFDEF] [ELSE] and [THEN] are simply Forth words that swallow the 
input unless the condition is met.

I suspect it will be similar to the bbranch & friends Fcode instructions 
whereby at compile time the current nested state is held on the dstack.

HTH,

Mark.

[Andreas Färber]

Am 02.12.2010 um 12:25 schrieb Mark Cave-Ayland:
> Andreas Färber wrote:
> > Hello,
> > A construct like:
> > [IFDEF] CONFIG_PPC
> >  [IFDEF] CONFIG_PPC64
> >    5
> >  [ELSE]
> >    4
> >  [THEN]
> > [ELSE]
> >  [IFDEF] CONFIG_SPARC64
> >    6
> >  [ELSE]
> >    3
> >  [THEN]
> > [THEN]
> > has been seen to return, e.g., 4 3 according to the debug word.
> > Is this nesting forbidden in Forth? Easily fixable? A better way to  
> > do this? I do want a final catch-all since returning no value would  
> > have unexpected results, and we currently do not have a define  
> > CONFIG_PPC32 so that a concatenation of independent [IFDEF]... 
> > [THEN]s wouldn't work.
>
> IIRC [IFDEF] [ELSE] and [THEN] are simply Forth words that swallow  
> the input unless the condition is met.
>
> I suspect it will be similar to the bbranch & friends Fcode  
> instructions whereby at compile time the current nested state is  
> held on the dstack.

I don't really understand the code in forth/lib/preprocessor.fs but it  
looks as if some state is held in three variables. Also the [ELSE]  
case handling in the [IF] loop looks unintuitive...

http://repo.or.cz/w/openbios/afaerber.git/blob/HEAD:/forth/lib/preprocessor....

Andreas

[Segher Boessenkool]

> I don't really understand the code in forth/lib/preprocessor.fs but it
> looks as if some state is held in three variables. Also the [ELSE]
> case handling in the [IF] loop looks unintuitive...

It looks like a bastardised version of the example code in the standard.
It only handles nested [IF] , not [IFDEF] etc.  It wouldn't be hard to
add it (just add and extra case, where it does a string compare for
[IF] ).

Segher

[Segher Boessenkool]

> > I don't really understand the code in forth/lib/preprocessor.fs but it
> > looks as if some state is held in three variables. Also the [ELSE]
> > case handling in the [IF] loop looks unintuitive...
>
> It looks like a bastardised version of the example code in the standard.
> It only handles nested [IF] , not [IFDEF] etc.  It wouldn't be hard to
> add it (just add and extra case, where it does a string compare for
> [IF] ).

Or, write it as

[DEFINED] bla [IF]
[DEFINED] blub [IF]
...
[ELSE]

etc.

Segher

[Andreas Färber]

Am 04.12.2010 um 03:16 schrieb Segher Boessenkool:
> > I don't really understand the code in forth/lib/preprocessor.fs but  
> > it
> > looks as if some state is held in three variables. Also the [ELSE]
> > case handling in the [IF] loop looks unintuitive...
>
> It looks like a bastardised version of the example code in the  
> standard.
> It only handles nested [IF] , not [IFDEF] etc.  It wouldn't be hard to
> add it (just add and extra case, where it does a string compare for
> [IF] ).

Thanks for the hint, working nicely now!

Andreas