Ambiguous non-terminal in GLR

Maxim Reznik <>
Mon, 01 Apr 2013 11:16:51 +0300

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Ambiguous non-terminal in GLR (Maxim Reznik) (2013-04-01)
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From: Maxim Reznik <>
Newsgroups: comp.compilers
Date: Mon, 01 Apr 2013 11:16:51 +0300
Organization: NNTP Server
Keywords: parse, question
Posted-Date: 02 Apr 2013 13:02:28 EDT

Hi, all

I'm playing with GLR and have a question.

When GLR parser reduces some text to the same non-terminal in two or
more ways it merges parse subtrees. Rekers uses 'symbol nodes' for this.

I this not each non-terminal could cause a merge. Knowing in advance
what non-terminals never merge will greatly simplify parse tree

For instance in Elkhound Technical Report the author implemented C++
grammar for GLR parser. He describes it:

        The grammar currently has 37 shift/reduce conflicts, 47
reduce/reduce conflicts and 8 ambiguous nonterminal.

How can I separate ambiguous and unambiguous nonterminal for a given
CFG? Where can I read about this?

Thank you
Maxim Reznik

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