Re: Interactive parsing with Bison

[Hans Aberg]

On 25 Jun 2006, at 01:23, Richard Stallman wrote:

> How about making GDB act as the interface for debugging Bison
> grammars?  GDB already has an IDE, through Emacs.

Paul Eggert had some ideas in the Bison Patches list that were not  
cc'ed to you.

> Another idea occurs to me: generate a function for each state, just to
> have a place to put a breakpoint corresponding to that state.  Right
> now, Bison generates code for each rule, and that's all.  That makes
> grammars compact, which is good for ordinary execution.  However,
> having a piece of code for each state could facilitate using GDB as
> the debugging interface.
>
> The function's source code could hold whatever information you want
> to present about that state, for debugging purposes.
>
> By continuing this idea, maybe you could set it up so that any C  
> debugger
> is a good debugger for Bison parsers.

As such, I think that an ordinary C-debugger might be used to debug  
the Bison parsing, displaying the exact position in the .y file in a  
GUI, but there needs to be two extensions, I think:

First, the debugger IDE must be able to display multiple arrows, as  
though there were multiple program counters in each function call.  
The reason for this, is because parsing proceeds over sets of rules,  
with a parsing position marked in each of them. (This is the stuff  
displayed in the Bison generated .output file of each state.)

Second, IDE's are often limited at displaying only one position per  
input source code line. 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.

  Hans Aberg