// quicksort

qsort(L) = qsort(L, []);

qsort([], Continuation) => Continuation;

qsort([A | L], Continuation) =>
  Below = keep(<(A), L),
  Above = keep(>=(A), L),
  qsort(Below, [A | qsort(Above, Continuation)]);

test_qsort() = qsort(prefix(24, random(1, 24)));