Re: [Gawkextlib-users] New API

[Andrew J. S. <as...@te...>]

Hi Jürgen,

On Fri, Jun 25, 2021 at 10:09:54AM +0200, Jürgen Kahrs via Gawkextlib-users wrote:
> I think he wants to detect the presence (and not the value) of a
> certain AWK rule at run-time. The term "rule" here seems to mean
> a keyword that exists after being declared by the plugin.

I'm not sure that I understand what "rule" means in an awk script.
>From the POSIX spec:

https://pubs.opengroup.org/onlinepubs/9699919799/utilities/awk.html

   An awk program is composed of pairs of the form:

   pattern { action }

So what's a "rule"? In the source code, it appears that the word "rule"
is used to refer to the combination of a pattern and an action. So
is the idea that this API hook would depend on detecting whether a combined
pattern & action is present?

> I agree with you (Andrew) that the script example that he gave
> should be accompanied by a more detailed implementation of
> the plugin. Maybe it would suffice to have a way of looking up
> all the keywords that are defined after loading a plugin.

The implementation of BEGINFILE and ENDFILE requires a lot of
special support in the interpreter. It seems to me that implementing
this sort of thing requires diving into the guts of how a program
is compiled in awkgram.y, which is quite frankly an area of the
code that I've never messed with. In main.c, the program is parsed
into code_block:

INSTRUCTION *code_block = NULL;
...
        /* Read in the program */
        if (parse_program(& code_block, false) != 0 || dash_v_errs > 0)
                exit(EXIT_FAILURE);

And then it runs the program by calling interpret(code_block).

So any info about the running program would have to be extracted by
parsing the INSTRUCTION data pointed to by code_block, as far
as I can tell.

Regards,
Andy