Naive quicksort implementation

gistfile1.erl

less_than(List, Pivot) ->
        less_than(List, Pivot, []).
        
less_than([], Pivot, Acc) ->
        Acc;
less_than([H|T], Pivot, Acc) when H < Pivot ->
        less_than(T, Pivot, [H|Acc]); 
less_than([H|T], Pivot, Acc) when H >= Pivot ->
        less_than(T, Pivot, Acc). 

greater_than(List, Pivot) ->
        greater_than(List, Pivot, []).

greater_than([], Pivot, Acc) ->
        Acc;
greater_than([H|T], Pivot, Acc) when H >= Pivot ->
        greater_than(T, Pivot, [H|Acc]);
greater_than([H|T], Pivot, Acc) when H < Pivot ->
        greater_than(T, Pivot, T).

%% quicksort
quicksort([]) -> [];
quicksort([Pivot|Rest]) ->
        lists:flatten([quicksort(less_than(Rest, Pivot)) , Pivot , quicksort(greater_than(Rest, Pivot))]).