Source code in the seed7 programming language

const proc: double (inout integer: a) is func
  begin
    a *:= 2;
  end func;

const proc: halve (inout integer: a) is func
  begin
    a := a div 2;
  end func;

const func boolean: even (in integer: a) is
  return not odd(a);

const func integer: peasantMult (in var integer: a, in var integer: b) is func
  result
    var integer: result is 0;
  begin
    while a <> 0 do
      if not even(a) then
        result +:= b;
      end if;
      halve(a);
      double(b);
    end while;
  end func;