Second maximum value

Hello

I'm new to postgres and I have tried to write a function which returns 
the second(third...) maximum to use it in a aggregation. But it's not 
function and I have no clue whats wrong.

Here what I do:

create type counter_max as (
maximum real,
value int );

create function get_counter_max(real, int) returns counter_max as 
'select $1, $2' language sql;

create or replace function x_max(counter_max, real) returns counter_max as '
declare   maxi alias for $1;   value alias for $2;   result counter_max; begin   if maxi.counter = 0 then   return
maxi;  elsif value >= maxi.maximum then     result.maximum := value;     result.counter := maxi.counter -1;     return
result;  else     return maxi;   end if; end; ' language 'plpgsql';
 

When I execute:  select x_max(get_counter_max(1., 1), 2.::real); it says:

WARNING:  plpgsql: ERROR during compile of x_max near line 11
ERROR:  return type mismatch in function returning tuple at or near "result"

Thanks in advance

Marco