%destructor is not compatible with YYSTYPE

[Mike Ady]

Sirs,

I was suffering from memory leaks when parsing bad input.  I added a
"%distructor" derective to my parser, but the resulting code would not
compile.  (I am working in C, with the MSVC++ 6 compiler.)  For example, I
added the following code:

%destructor {  freetoken($$); } MYTOK_INTEGER  ...

Then Bison generated the following destructor code for each token type I
specified:

freetoken(yyvaluep->(null));

That code is invalid and it caused my C compiler to issue an error message.
The problem appears to be that I was declaring the parser value data type
with YYSTYPE instead of with %union.

I first got my parser working by hacking the output .tab.c file, and
replacing the above code with

#define YYSTYPE struct mytok *
...
freetoken((YYSTYPE)*yyvaluep);

Then I discarded my YYSTYPE definition and switched to a %union directive.
That solved the problem (and no more memory leaks!).

I don't know if this is a bug or an undocumented feature/restriction.  But
it looks like support for YYSTYPE was missed as an oversight.

Regards,
Mike Ady