Naive qsort in Erlang.

sort.erl

-module(sort).
-export([qsort/1]).
 
%%% A slightly naive implementation. But at least it does partial TCO.
 
partition(_, [], Smaller, Equal, Larger) -> {Smaller, Equal, Larger};
partition(Pivot, [H|T], Smaller, Equal, Larger) when H < Pivot -> partition(Pivot, T, [H|Smaller], Equal, Larger);
partition(Pivot, [H|T], Smaller, Equal, Larger) when H =:= Pivot -> partition(Pivot, T, Smaller, [H|Equal], Larger);
partition(Pivot, [H|T], Smaller, Equal, Larger) when H > Pivot -> partition(Pivot, T, Smaller, Equal, [H|Larger]).
 
qsort(L) -> qsort(L, []).
 
qsort([], Acc) -> Acc;
qsort([H|T], Acc) ->
	{A,B,C} = partition(H,T,[],[H],[]),
	qsort(A, B ++ qsort(C, Acc)).