map.sql

CREATE OR REPLACE FUNCTION eval(_ anyelement, proc Text) RETURNS anyelement AS $$
    BEGIN
        EXECUTE 'SELECT ' || replace(proc, '_', _::text) INTO $0;
        RETURN $0;
    END;
$$ LANGUAGE plpgsql;


CREATE OR REPLACE FUNCTION map(ary anyarray, proc Text) RETURNS anyarray AS $SQL$
    SELECT array_agg(eval(_, proc))
    FROM unnest(ary) AS _
$SQL$ LANGUAGE sql;

select map(ARRAY[1,2,3]::int[], '_ + 1');

   map
---------
 {2,3,4}
(1 row)