Prepared statements in PGSQL functions

Hi Listers,
I want to use prepared statement in a function. Here is my code:

create or replace function  generate_data ( integer, integer )
returns integer
as
$BODY$    declare     p_count         alias for $1;    p_max_value_id1 alias for $2;    v_max_value_id1 integer  ;
v_id1int;    v_id2 int;    v_filler varchar(200) := repeat('BIGSTRING', 3);begin    v_id1:= round(  (random()*
v_max_value_id1)::bigint,0);   v_id2:= round(  (random()* v_max_value_id1)::bigint,0);    prepare  mystmt( int, int,
varchar)   as insert into part values ($1,$2,$3);    execute  mystmt(v_id1, v_id2, v_filler );    deallocate
mystmt;end;
$BODY$
language plpgsql ; 


Definition of table part is :

CREATE TABLE part (   id1    int not null,   id2    int not null,   filler varchar(200)   );


When I try to  call my function I am getting the following errors :
postgres=# select  * from  gen (10, 10 );
ERROR:  function mystmt(integer, integer, character varying) does not exist
HINT:  No function matches the given name and argument types. You may need to add explicit type casts.
CONTEXT:  SQL statement "SELECT  mystmt( $1 ,  $2 ,  $3  )"
PL/pgSQL function "gen" line 12 at execute statement


How to solve my problem ? Is it possible at all to call prepared statement inside a function at all?


Regards. MILEN