oracle date format error handling

SELECT ab.* from WuZKCXX ab WHERE ab.shixrq IS NOT NULL AND fun_date_YorN(ab.shixrq) = 0

create or replace function fun_date_YorN(i_dt varchar2) return number is
v_dt date;
begin
v_dt := to_date(i_dt, 'yyyy-mm-dd');
return 1;
exception
when others then
return 0;
end fun_date_YorN;