defining a parameter by referring to the components of a set

Hi,
I need to define a parameter that should be defined over values of the first components of the elements of a set:

set CG within {STATE,ACTION};
param state_c {s in CG[1]} ???

Essentially, the parameter state_c should be defined for all possible values of the first component of the elements of the set CG. When CG= {(1,1), (2,1), (3,2)}, I should have state_c[1], state_c[2], and state_c[3]. (I am updating the set CG during the implementation of the algorithm, so the elements of CG are dynamic)

Does anyone know how to do this?

Thanks alot,