code.erl

merge(A, []) -> {A, 0};
merge([], B) -> {B, 0};
merge([Ha|Ta], [Hb|Tb]) ->
    if
        Ha < Hb -> {MergedList, N}=merge(Ta, [Hb|Tb]),
                   {[Ha | MergedList], N};
        true -> {MergedList, N}=merge([Ha|Ta], Tb),
                {[Hb | MergedList], N + 1}
    end.

pMergeSort(L) when length(L) == 1 -> L;
pMergeSort(L) when length(L) > 1 ->
    {L1, L2} = lists:split(length(L) div 2, L),
    spawn(main, pMergeSort2, [L1, self()]),
    spawn(main, pMergeSort2, [L2, self()]),
    mergeResults().

pMergeSort2(L, Parent) when length(L) == 1 -> 
    Parent ! L;
pMergeSort2(L, Parent) when length(L) > 1 ->
    {L1, L2} = lists:split(length(L) div 2, L),
    spawn(main, pMergeSort2, [L1, self()]),
    spawn(main, pMergeSort2, [L2, self()]),
    Parent ! mergeResults().

mergeResults() ->
    L1 = receive
             Res -> Res
         end,
    L2 = receive
             Res -> Res
         end,
    {MergedList, N} = merge(L1, L2),
    MergedList.

% Call pMergeSort(IndexedList).