Re: Type checking in semantic actions

[Hans Aberg]

On 13 Feb 2010, at 22:45, Michael Budach wrote:

> 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.

Bison just implements the %union default rule as untyped $$ = $1, that  
is, the types only exist as static checking in the Bison compile, and  
not in the output parser code. (For C++, Akim has implemented  
variants, to appear in Bison 2.6, where the type also exits in the C++  
code, but suspect you do not need it.)

So you need to assign config_spec a valid value somewhere, or write a  
rule that initializes $$ instead of the default rule.

  Hans