Extrair data do oráculo de string

SELECT  TO_DATE(
          REGEXP_SUBSTR(
            'Chicago, IL, April 20, 2015 — and so on text here',
            '(JANUARY|FEBRUARY|MARCH|APRIL|MAY|JUNE|JULY|AUGUST|SEPTEMBER|'
              || 'OCTOBER|NOVEMBER|DECEMBER)'
              || '[[:space:]]+([012]?[0-9]|3[01])'
              || '[[:punct:][:space:]]+\d{4}',
            1,
            1,
            'i'
          ),
          'MONTH DD YYYY'
        )
FROM    DUAL;

CREATE FUNCTION parse_Date(
  in_string     VARCHAR2,
  in_format     VARCHAR2 DEFAULT 'YYYY-MM-DD',
  in_nls_params VARCHAR2 DEFAULT NULL
) RETURN DATE DETERMINISTIC
AS
BEGIN
  RETURN TO_DATE( in_string, in_format, in_nls_params );
EXCEPTION
  WHEN OTHERS THEN
    RETURN NULL;
END;
/