Scaler forms as function arguments

Hi,

I want to write a function of the following type
  CREATE FUNCTION test ( <scalar form type> )        RETURNS setof MyTable        AS        'SELECT * FROM MyTable
WHEREid IN $1'        LANGUAGE 'SQL' ;
 

I was not able to find a reference whether this is possible and if yes
how to specify the argument type and how to call this function to hand over
the list for the IN clause correctly.

Next question.  Is there any example how to return a SETOF MyTable in
a plpgsql function?  I tried
CREATE FUNCTION test2()   RETURNS setof MyTable   AS '   DECLARE      result   SETOF MyTable ;   BEGIN     result :=
(SELECT* FROM MyTable);     RETURN result ;   END; ' LANGUAGE 'plpgsql';
 

wich failed.

Kind regards
        Andreas.