My guess is that you have a precedence error in your print statement. Add some parens:

print(defined($parser->startrule($mw2->get ("1.0", "500.0")))
? "NO ERROR\n" : "ERROR");
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Correction: no precedence error in the original.

Although, even if that fixes one problem, it may not be the end of your woes.

You may find the posts in this recent meditation enlightening.

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