creating a function in psql

hi,

i'm trying to create a very basic function in psql and i keep getting
the error:
QUERY: CREATE FUNCTION add_one () RETURNS int4 AS '
    BEGIN
        RETURN 1 + 1;
    END;
' LANGUAGE 'plpgsql';
ERROR:  Unrecognized language specified in a CREATE FUNCTION:
'plpgsql'.  Recognized languages are sql, C, internal and the created
procedural languages.

does anyone know how i can get this language to be recognized?

also, this is probably related, i was trying to set the date string
using
SET DATESTYLE

and it doesn't seem to know what i'm talking about.

can anyone help??? thanks so much in advance,

rachel