Shuffle

   if L == nil then nil
   else
      local Length A L2 in
     {List.length L Length}
     A = {NewArray 1 Length 0}
     L2 = {NewCell nil}

     for J in 1..Length do
        local Na in
        {List.nth L J Na}
           A.J := Na
        end
     end

     for J2 in 1..Length do
        local I J in
           J = Length + 1 - J2
           I = {Number.abs ({OS.rand} mod J) } + 1
           L2 := A.I|@L2
           A.I := A.J
        end
     end

     @L2
      end
   end