37815.pas(20,10) Fatal: Syntax error, ']' expected but '..' found

37815.pas(20,10) Fatal: Compilation aborted
var
  i,n,s:longint;
  a:array[0..1023]of integer;
  ch:char;
procedure d(da:array of integer;dn:longint);
  var
    dt,dy,di:longint;
  begin
    if dn=1 then
      begin
        if da[0]=1 then write('I')
        else write('B');
        exit;
      end;
    dt:=0;
    dy:=0;
    for di:=0 to dn-1 do
      if da[di]=1 then dy:=1
      else dt:=1;
    d(da[0..dn div 2-1],dn div 2);
    d(da[dn div 2..dn-1],dn div 2);
    if (dt=1) and (dy=1) then write('F')
    else if dt=0 then write('I')
         else write('B');
  end;
begin
  readln(n);
  s:=1;
  for i:=1 to n do
    s:=s*2;
  for i:=0 to s-1 do
    begin
      read(ch);
      a[i]:=ord(ch)-ord('0');
    end;
  d(a,s);
end.
在pascal上都可以啊