discussion about OpenBIOS - a free portable firmware implementation ()

Andreas Färber | 4 Dec 2010 01:11

Re: Nested [IFDEF]s not working?

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

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Segher Boessenkool | 4 Dec 2010 03:16

Re: Nested [IFDEF]s not working?

> 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

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Segher Boessenkool | 4 Dec 2010 03:26

Re: Nested [IFDEF]s not working?

>> 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

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Andreas Färber | 4 Dec 2010 12:35

Re: Nested [IFDEF]s not working?

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