ALTER SESSION SET PLSQL_OPTIMIZE_LEVEL = 3

ALTER SESSION SET PLSQL_CODE_TYPE      = 'NATIVE'

CREATE OR REPLACE PROCEDURE RAGTEST 
AS 
    FUNCTION is_nls_date 
      ( p_string        IN VARCHAR2 
      , p_format_mask   IN VARCHAR2 
      ) 
    RETURN NUMBER 
    AS 
        l_test   DATE; 
        l_return NUMBER := 0; 
    BEGIN 
        BEGIN 
            l_test   := TO_DATE(p_string, ''''||p_format_mask||''''); 
            l_return := l_test-l_test+1; 
        EXCEPTION 
            WHEN OTHERS THEN 
                l_return := 0; 
        END; 
        -- 
        RETURN l_return; 
    END is_nls_date; 
BEGIN 
    DBMS_OUTPUT.PUT_LINE('is_date 01.01.xxxx = '||is_nls_date('01.01.xxxx','DD.MM.YYYY')); 
    DBMS_OUTPUT.PUT_LINE('is_date 01.01.2001 = '||is_nls_date('01.01.2001','DD.MM.YYYY')); 
END; 

exec ragtest