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Asked: 2026-06-13T23:12:01+00:00

My problem is that the message passed to yyerror is already formatted (i.e. it

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My problem is that the message passed to yyerror is already formatted (i.e. it is actually an English explanation what went wrong), and what I would like to get is just the current token (i.e. the one before the error pseudo-token).

So how to get it?

I use gplex/gppg which are lex/yacc implementations in C#.

I am sorry for not being 100% precise — what I need is token (symbol) not the body (text) which was matched (by the token).

Let’s say I have a rule [A-Za-z0-9_]+ constitutes an ID. So I would like to get token ID not a foobar.

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1 Answer

  1. Editorial Team

    There’s no standard, but bison and most versions of yacc store the current token in yychar. Unfortunately, this is generally a local variable (of yyparse), so you can’t access it in other functions (such as yyerror), only in parser actions.

    It might be helpful if you say WHY you want the current token — its not generally a useful peice of information. You mention the error pseudo-token, which makes no sense as that is associated with error recovery, not errors as such — by the time it comes into the picture normally a bunch of tokens from the input have been discarded.

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