function does not exist error...

Can someone help me figure out why my trigger can't meet my function?
Other than the obvious reason that I'm a total beginner, and I don't
know what the heck I'm doing. :-)

After I got the CreateTrigger error, I reran the CreateFunction query
just to see what would happen:

recordings=> CREATE FUNCTION check_participant(varchar) RETURNS opaque AS '
DECLARE name ALIAS FOR $1;
BEGIN
SELECT fname FROM participant WHERE fname = name; IF FOUND
THEN RETURN 0;
ELSE INSERT INTO artist (fname) VALUES (name); END IF; END;'
LANGUAGE 'plpgsql';

ERROR: function check_participant already exists with same argument types

recordings=> CREATE TRIGGER trigger_artist BEFORE INSERT ON participant
FOR EACH ROW EXECUTE PROCEDURE check_participant();

ERROR: CreateTrigger: function check_participant() does not exist