plpgsql code doen't work

Hi, 
 
I found following code:

create or replace function plpgsql_edit_distance(stra text, strb text)
returns integer as $$
declare
rows integer;
cols integer;
begin
rows := length(stra);
cols := length(strb);

IF rows = 0 THEN
return cols;
END IF;
IF cols = 0 THEN
return rows;
END IF;

declare
row_u integer[];
row_l integer[];
diagonal integer;
upper integer;
left integer;
begin
FOR i in 0..cols LOOP
row_u[i] := i;
END LOOP;

FOR i IN 1..rows LOOP
row_l[0] := i;
FOR j IN 1..cols LOOP
IF substring (stra, i, 1) = substring (strb, j, 1) THEN
diagonal := row_u[j-1];
else
diagonal := row_u[j-1] + 1;
END IF;
upper := row_u[j] + 1;
left := row_l[j-1] + 1;
row_l[j] := int4smaller(int4smaller(diagonal, upper), left);
END LOOP;
row_u := row_l;
END LOOP;
return row_l[cols];
end;
end
$$ language 'plpgsql' immutable strict;

Does anyone know why the colums :"row_l[j] := int4smaller(int4smaller(diagonal, upper), left);" doesn't work.
 
Janek Sendrowski