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copied!<p>So I spent a reasonable amount of time picking over the grammar (and the bison output) and can't see what is obviously wrong here. Without having the means to execute it, I can't easily figure out what is going on by experimentation. Therefore, here are some concrete steps I usually go through when debugging grammars. Hopefully you can do any of these you haven't already done and then perhaps post follow-ups (or edit your question) with any results that might be revealing:</p> <ol> <li>Contrive the smallest (in terms of number of tokens) possible working input, and the smallest possible non-working inputs based on the rules you expect to be applied.</li> <li>Create a copy of the grammar file including only the troublesome rules and as few other supporting rules as you can get away with (i.e. you want a language that only allows construction of sequences consisting of the <code>object</code> and <code>more_object</code> rules, joined by ARROW. Does this work as you expect?</li> <li>Does the rule in which it is nested work as you expect? Try replacing <code>object</code> with some other very simple rule (using some tokens not occuring elsewhere) and seeing if you can include those tokens without it breaking everything else.</li> <li>Run bison with <code>--report=all</code>. Inspect the output to try to trace the rules you've added and the states that they affect. Try removing those rules and repeat the process - what has changed? This is extremely time consuming often, and is a giant pain, but it's a good last resort. I recommend a pencil and some paper.</li> </ol> <p>Looking at the structure of your error output - '+' is being recognised as an identifier token, and is therefore being looked up as a symbol. It might be worth checker your lexer to see how it is processing identifier tokens. You might just accidentally be grabbing too much. As a further debugging technique, you might consider turning some of those token literals (e.g. '+', '{', etc) into real tokens so that bison's error reporting can help you out a little more.</p> <p>EDIT: OK, the more I've dug into it, the more I'm convinced that the lexer is not necessarily working as it should be. I would double-check that the stream of tokens you are getting from yylex() matches your expectations before proceeding any further. In particular, it looks like a bunch of symbols that you consider special (e.g. '+' and '{') are being captured by some of your regular expressions, or at least are being allowed to pass for identifiers.</p>

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