$ include "seed7_05.s7i";
  include "float.s7i";
  include "math.s7i";

const func float: entropy (in string: stri) is func
  result
    var float: entropy is 0.0;
  local
    var hash [char] integer: count is (hash [char] integer).value;
    var char: ch is ' ';
    var float: p is 0.0;
  begin
    for ch range stri do
      if ch in count then
        incr(count[ch]);
      else
        count @:= [ch] 1;
      end if;
    end for;
    for key ch range count do
      p := flt(count[ch]) / flt(length(stri));
      entropy -:= p * log(p) / log(2.0);
    end for;
  end func ;

const proc: main is func
  begin
    writeln(entropy("1223334444") digits 5);
  end func;