mylist.erl

-module(mylist).
-export([append/2, sum/1]).

append([H|T], Tail) ->
    [H] ++ append(T, Tail);
append([], Tail) ->
    [Tail].

sum([H|T]) -> H + sum(T);

sum([]) -> 0.

mysort.erl

-module(mysort).
-export([sort/1]).

partition(_, [], Smaller, Larger) -> {Smaller, Larger};

partition(Pivot, [H|T], Smaller, Larger) ->
    if H =< Pivot -> partition(Pivot, T, [H|Smaller], Larger);
       H >  Pivot -> partition(Pivot, T, Smaller, [H|Larger])
    end.

sort([]) -> [];

sort([Pivot|Rest]) ->
    {Smaller, Larger} = partition(Pivot, Rest, [], []),
    sort(Smaller) ++ [Pivot] ++ sort(Larger).