Sorter: func [List /local Piv OnPiv][
   if 2 > length? List [return List]
   Piv: List/1
   OnPiv: array/initial (subtract (length? List) (length? remove-each I copy List [I = Piv])) Piv
   return compose [
      (Sorter remove-each I copy List [I >= Piv])
      (OnPiv)
      (Sorter remove-each I copy List [I <= Piv])
   ]
]