Не компиляется процедура

CREATE TABLE TBL_MKB10 (
    ID          INTEGER NOT NULL,
    PARENT_ID   INTEGER,
    MKB_VALUES  VARCHAR(300)
);

ALTER TABLE TBL_MKB10 ADD CONSTRAINT PK_MKB10 PRIMARY KEY (ID);
CREATE INDEX PARENT_IDX ON TBL_MKB10 (PARENT_ID);

CREATE OR ALTER PROCEDURE GET_PARENT (
    ID TYPE OF COLUMN TBL_MKB10.ID)
RETURNS (
    PATH TYPE OF COLUMN TBL_MKB10.MKB_VALUES,
    PARENT_ID TYPE OF COLUMN TBL_MKB10.PARENT_ID)
AS
BEGIN
  WHILE (:ID > 0) DO
  BEGIN
    FOR SELECT M.PARENT_ID, M.MKB_VALUES
        FROM TBL_MKB10 M
        WHERE M.ID = :ID
        INTO :PARENT_ID, :PATH; --вероятно, затык тут
        ID = :PARENT_ID;
        SUSPEND;
      END
END

Invalid token.
Dynamic SQL Error.
SQL error code = -104.
Token unknown - line 13, column 31.
;.