HOW-TO do incomplete dates: year, optional month, optional day?

is there a way, save lots of manual manipulation and
hand-waving, to implement PARTIAL DATES? (this may be exactly
the job for creating a new data type, but hopefully someone's
already invented this wheel...?)

    "doug has worked at pinnacle since 1991".

not 1-jan-1991, not 31-dec-1991, but just plain-ol' 1991.

    "beulah started here back in november of 1998."

not 1-november, not 30-november. just november, of 1999.

    "my first day at acme corp was the 17th of may, 2001."

here, in that same field, we need year, month AND day.

at the moment i'm considering views and rules (with plpgsql
functions to do the re-assembly). here's a seat-of-the-pants
recreation (no syntax checking) to show my gyrations:

CREATE TABLE partial_dates(
    -- yada yada
    partial_year  INTEGER, -- zero/null or 1492, 2001...
    partial_month SMALLINT,-- zero/null, or 1-12
    partial_day   SMALLINT -- zero/null, or 1-31
    -- yada yada
);

CREATE FUNCTION
    partial_date(integer,smallint,smallint) -- y,m,d
RETURNS TEXT as '
DECLARE
    yr ALIAS FOR $1;
    mo ALIAS FOR $2;
    dy ALIAS FOR $3;
    month TEXT;
BEGIN
    IF yr < 1900 THEN
        RETURN ''UNKNOWN'';
    END IF;
    IF mo < 1 THEN
        RETURN yr || text;
    END IF;
    SELECT INTO month abbr_en FROM month_table WHERE num = mo;
    IF dy < 1 THEN
        RETURN yr::text || ''-'' || month;
    END IF;
    RETURN yr::text || ''-'' || month || ''-'' || dy::text;
END;
' language 'plpgsql';

CREATE VIEW dates AS
SELECT
    -- yada yada
    partial_date(partial_year, partial_month, partial_day)
    -- yada yada
FROM
    partial_dates;

is there a better way?

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