struct psi_let_callback *psi_let_callback_init(struct psi_let_func *func, struct psi_plist *args, struct psi_plist *cb_args);
void psi_let_callback_free(struct psi_let_callback **cb_ptr);
struct psi_let_callback *psi_let_callback_init(struct psi_let_func *func, struct psi_plist *args, struct psi_plist *cb_args);
void psi_let_callback_free(struct psi_let_callback **cb_ptr);