Forms :: How To Pass Table Name By Reference To Function

I have to create a function which count the max id in the provided table.

For example: I have two table customer and book

and

create or replace function Row_Count(tab_nam) return varchar2 is

CONTR_NO varchar2;
begin
select NVL(MAX(t.contract_num), 0) + 1
INTO CONTR_NO
FROM tab_nam t;
return(CONTR_NO);
end Row_Count;

when I call

Function( customer) ;
or
Function( book) ;

It should tell the max number with addition of one.