"Surface" calls in light shaders

Hi all , does something like this have any sense ?

    code:
    light
    surfLight(
            float intensity = 1;
            color lightcolor = 1;
            point from = point "shader" (0,0,0);
            )
    {
      illuminate(from) {
       color surfaceCol ;
       float getme = surface( "_diffuse" , surfaceCol );
       printf ( "%f %c \n", getme , surfaceCol ) ;
          Cl += surfaceCol; // it should look twice as bright
    }
    }



It seems like i get nothing returning from the

    code:
     surface( "_diffuse" , surfaceCol )

call (the _diffuse component is an output color of a surface shader)?
Thanks ,
STe