plpgsql language not recognized

I am trying to create a function, and I am getting the following error
message:

ERROR: Unrecognized language specified in a CREATE FUNCTION:
'plpgsql'. Recognized languages are sql, C, internal and the created
procedural languages.

This is the text of the function:

CREATE FUNCTION rational (int1, int2) RETURNS text AS '
DECLARE
numerator ALIAS FOR $1;
denominator ALIAS FOR $2;
txtRational text;
BEGIN
txtRational := to_char(numerator,''999999'');
RETURN txtRational;
END;
' LANGUAGE 'plpgsql';

This is my first function, and obviously it isn't complete yet. It is
supposed to take two integer values, used to store the numerator and
denominator of a rational value, and return it as a string in the form
'numerator/denominator' when it is finished.

Any help much appreciated.

tia,
David

--
Dr. David C. Merrill http://www.lupercalia.net
Linux Documentation Project dmerrill(at)lupercalia(dot)net
Collection Editor & Coordinator http://www.linuxdoc.org
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