sql insert function

The documentation doesn't have any examples of using an sql language
function to do an insert, andI am at loss as to I am doing wrong here.
The error I get trying to create the function is: ERROR: syntax error at
or near "$1" at character 148

CREATE FUNCTION taxship(varchar,integer,varchar,float,float) returns integer
AS '
insert into taxship(s_oid,order_id,mer_id,tax,shipping) values
('$1',$2,'$3',$4,$5);
SELECT 1;
' LANGUAGE SQL;