const func bigInteger: fib (in integer: number) is func
  result
    var bigInteger: result is 1_;
  local
    var integer: i is 0;
    var bigInteger: a is 0_;
    var bigInteger: c is 0_;
  begin
    for i range 1 to pred(number) do
      c := a;
      a := result;
      result +:= c;
    end for;
  end func;