+b4_error_verbose_if([state_type yystate, const symbol_type& yyla],
+ [state_type, const symbol_type&])[) const
+ {]b4_error_verbose_if([[
+ // Number of reported tokens (one for the "unexpected", one per
+ // "expected").
+ size_t yycount = 0;
+ // Its maximum.
+ enum { YYERROR_VERBOSE_ARGS_MAXIMUM = 5 };
+ // Arguments of yyformat.
+ char const *yyarg[YYERROR_VERBOSE_ARGS_MAXIMUM];
+
+ /* There are many possibilities here to consider:
+ - If this state is a consistent state with a default action, then
+ the only way this function was invoked is if the default action
+ is an error action. In that case, don't check for expected
+ tokens because there are none.
+ - The only way there can be no lookahead present (in yyla) is
+ if this state is a consistent state with a default action.
+ Thus, detecting the absence of a lookahead is sufficient to
+ determine that there is no unexpected or expected token to
+ report. In that case, just report a simple "syntax error".
+ - Don't assume there isn't a lookahead just because this state is
+ a consistent state with a default action. There might have
+ been a previous inconsistent state, consistent state with a
+ non-default action, or user semantic action that manipulated
+ yyla. (However, yyla is currently not documented for users.)
+ - Of course, the expected token list depends on states to have
+ correct lookahead information, and it depends on the parser not
+ to perform extra reductions after fetching a lookahead from the
+ scanner and before detecting a syntax error. Thus, state
+ merging (from LALR or IELR) and default reductions corrupt the
+ expected token list. However, the list is correct for
+ canonical LR with one exception: it will still contain any
+ token that will not be accepted due to an error action in a
+ later state.
+ */
+ if (!yyla.empty ())
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