resource quick()

  op sort(var a[1:*]: int)  # forward declaration for sort()

  var n: int; getarg(1,n)
  var a[1:n]: int

  # read in data to be sorted
  fa i := 1 to n -> read(a[i]) af

  write("input:"); fa i := 1 to n -> write(a[i]) af
  sort(a)
  write("sorted:"); fa i := 1 to n -> write(a[i]) af

  proc sort(a)
    if ub(a) <= 1 -> write("small array", ub(a)); return fi
    fa i := 1 to ub(a) -> writes(a[i], " ") af; write()
    var pivot := a[1]
    var lx := 2, rx := ub(a)
    do lx <= rx ->
        if a[lx] <= pivot -> lx++
        [] a[lx] >  pivot -> a[lx] :=: a[rx]; rx--
        fi
    od
    a[rx] :=: a[1]
    co sort(a[1:rx-1]) // sort(a[lx:ub(a)]) oc
  end

end quick