struct psi_num_exp *psi_num_exp_init_binary(token_t op,
struct psi_num_exp *lhs, struct psi_num_exp *rhs);
struct psi_num_exp *psi_num_exp_init_unary(token_t op,
struct psi_num_exp *psi_num_exp_init_binary(token_t op,
struct psi_num_exp *lhs, struct psi_num_exp *rhs);
struct psi_num_exp *psi_num_exp_init_unary(token_t op,