Re: Interactive parsing with Bison

[Hans Aberg]

On 26 Jun 2006, at 06:03, Richard Stallman wrote:

>     Second, IDE's are often limited at displaying only one position  
> per
>     input source code line.
>
> I don't understand that sentence.

Perhaps things have changed, but the visual debuggers I used only  
displayed an arrow at the margin of the source code (like the .c  
files), indicating that the program counter is on that line, but with  
no further indication where it is within that line. If one would want  
to step through the code and see where the program counter is in such  
program code, one would have to break up the source code on several  
input lines, and recompile, so that the debugger can display it.

Now, with a .y grammar, this would be rather bothersome, as very  
often, each rule has several grammar symbols per line. So there, one  
wants, in addition to the arrows at the margin pointing out which  
rules are in the active state, an arrow within each line, indicating  
the parser position (as described in the .output file, in the state  
information).

>                             This would be insufficient for displaying a
>     parsing position in each grammar rule of the .y file, which  
> normally
>     has several symbols on the same line. So here, one needs an arrow
>     pointing between the grammar symbols of each active rule.
>
> We could surely modify GDB and gdb-ui.el to do that.

It could be that this feature is useful for C/C++ debugging as well.  
If the debugger is extended (if it does not already have the feature)  
to be able to display positions within each line as well, I think it  
is just the question of putting the right information in the debugger  
file format. In the past, perhaps debugger files would have been  
viewed as becoming to large, but computer space is nowadays is ample:  
It seems me one should ideally not have to change the source code, in  
order to do debugging.

  Hans Aberg