RecDescent error handling

dcorbin has asked for the wisdom of the Perl Monks concerning the following question:

I'm working on my first use of RecDescent (way-cool Damian). Consider this small piece of a grammar:

foo: bar
        {
            ::processBar($item1)
        }

Under certain circumstances (bad input) processBar will fail. Now, I understand that if I return undef, the production should fail, etc. What I want to do is be able to provide the error message that processBar() has "calculated". I tried adding <error: ${::getError()}> after the action, but that doesn't seem to have worked... What's the best way to do this. Should processBar just "print STDERR 'msg'"?

Comment on RecDescent error handling

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Re: RecDescent error handling by maverick (Curate) on Sep 05, 2000 at 23:28 UTC
well, you could store your error string in a scalar and then do something like. `foo: bar { return ::processBar($item[1]); # return undef on fail } \|<error: $error_string>` [download] There's probably a more elegant way of doing this, but this was the first thing that came to mind. :) /\/\averick	[reply] [d/l]
Re: RecDescent error handling by merlyn (Sage) on Sep 05, 2000 at 23:23 UTC
If I understand you, just have your subroutine change a global variable to be the error message, then look at that on an undef return. You can make it a list if you want to report more than one error. You also might want to look into the `<error:...>` directive for the grammar. -- Randal L. Schwartz, Perl hacker	[reply] [d/l]
RE: Re: RecDescent error handling by dcorbin (Sexton) on Sep 05, 2000 at 23:26 UTC
I did look into <error:>. I even tried to mention it above, though it apparently got eaten up as HTML so no one could see it. I'm apparently having a problem placing that directive where it gets activated only if the action fails.	[reply]
RE: RE: Re: RecDescent error handling by merlyn (Sage) on Sep 05, 2000 at 23:28 UTC
As the docs show, try something like: `foo: bar { ::myroutine($item{bar}) } # this may fail, returning undef \| <error: ... your message here >` [download] -- Randal L. Schwartz, Perl hacker	[reply] [d/l]