p_error parameters lack information

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Robert Grosse

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Oct 28, 2012, 10:15:14 PM10/28/12
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One can define a p_error function to handle syntax errors, but
unfortunately, Ply provides no useful information to the function. I've had
to resort to an ugly reflection hack just to provide meaningful error
messages. Would it be possible to improve the interface so that Ply
actually provides access to this information?

def p_error(p):
    if p is None:
        print "Syntax error: unexpected EOF"
    else:
        print "Syntax error at line {}: unexpected token
{}".format(p.lineno, p.value)

    #Ugly hack since Ply doesn't provide any useful error information
    import inspect
    frame = inspect.currentframe()
    cvars = frame.f_back.f_locals
    print 'Expected:', ', '.join(cvars['actions'][cvars[
'state']].keys())
    print 'Found:', cvars['ltype']
    print 'Current stack:', cvars['symstack']

David Beazley

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Oct 29, 2012, 6:56:33 PM10/29/12
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In the GIT repository for PLY, I refactored a bit of the error handling code to simplify a few things, but I think I could be convinced to expand it a bit more.    Let me think about how I would handle it.   Perhaps p_error() handling could be expanded to support an optional second argument in which the parser instance would be passed.   Certainly open to design ideas on this.

Cheers,
Dave


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p_error parameters lack information
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Erez

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Oct 30, 2012, 7:09:54 AM10/30/12
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I think that's a great idea.

I would not add an argument to p_error, because that would break backwards-compatibility.
Perhaps you could add a new method with extended information. Like
p_error_verbose(p, actions, state, stack)

(or if you wish to allow more information in the future, p_error_verbose(p, error_info_dict) ) 

David Beazley

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Oct 30, 2012, 7:34:59 AM10/30/12
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I like the idea of having an p_error_verbose() function.     That's definitely doable.  I'll work on it.

Cheers,
Dave

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Robert Grosse

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Oct 30, 2012, 9:37:26 AM10/30/12
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Why not make it take **kwargs rather than error_info_dict? That way it can easily be extended while allowing people to ignore arguments they don't care about.
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