[SQL] How to declare cursor if tablename is a variable?

[hu js]

See this:
“CREATE or replace function geo_polygon(tablename varchar) RETURNS integer 
AS $$
DECLARE
   objectid varchar;
   tab varchar;
   x1 float;
   y1 float;
   
   obj_num integer;
   point_num integer;
   polygonstr varchar;
   
   cur_obj CURSOR FOR SELECT mrc_xy_position FROM tablename;    
   cur_point CURSOR FOR SELECT x,y FROM tablename where mrc_xy_position = 
objectid;

BEGIN   
…….“

Error if call the function. Neither to use “execute” . Who can solve it? 
Thanks!

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