Bug in YACC discovered?

I offered someone to write a (small) compiler to be included
in his program. I use YACC, but I run into a strange problem.
My YACC-rules are mostly of the form:


nonterminal: A_TOKEN
{if (!some_test($1))
report("user friendly error message");
}
ANOTHER_TOKEN
{if (!another_test($3))
report("user friendly error message");
}
YET_ANOTHER_TOKEN AND_ANOTHER
{if (!still_more_tests($5,$6))
report("user friendly error message");
}
LAST_TOKEN
{final_actions();}
;
(Tab size is 4..., sorry);


The problem is that in the "final_actions" part, the value of
$1 is somehow overwritten. I encountered this in two different
places. Even if I write a rule like:


nonterm: TOKEN1
{printf($1);}
TOKEN2 TOKEN3 TOKEN4 TOKEN5
{printf($1);}
;


Now two different values are printed!


There is a lot of C-code between the tokens in my rules, but
this shouldn't change the $x values, does it?


Any ideas about what YACC thinks of this are welcome...


Eelco Vriezekolk
wsineel@lso.win.tue.nl

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