Type checking in semantic actions

[Michael Budach]

Hello folks

I am currently working on my first bison project, which is a parser for 
vhdl. Since I only need a subset of the language, I want to specify 
actions only this subset.

consider the following example:

arch_body_1  :  ;
        { $<Iface>$ = new TDataLineList; }
arch_body_1  : block_decltve_item;
        { $<Iface>$ = $<Iface>1; }
arch_body_1  : arch_body_1 block_decltve_item;
        { $<Iface>$ = appendToInterface($<Iface>1, $<Iface>2);        }

block_decltve_item    : common_decltve_item;
block_decltve_item    : subprog_body;
block_decltve_item    : comp_decl;
block_decltve_item    : attribute_decl;
block_decltve_item    : attribute_spec;
block_decltve_item    : config_spec;
block_decltve_item    : disconnection_spec;
block_decltve_item    : signal_decl  { $<Iface>$ = $<Iface>1; }


I implemented actions only for the signal_decl stuff, which returns an 
Iface*. This means when e.g. a comp_decl occurs in the input, the 
program crashes in the arch_body_1 actions, becuase they don't get an 
Iface* but (in my case) a   keyword (char*).

How can I determine of which type or which token-type an argument $n is? 
I tried a dynamic_cast, but this does not work with unions and I don't 
want to implement 'dummy' actions for all rules which i want to ignore.

Thanks for you help

Best regards,
Michael