lib_misc.erl

-module(lib_misc).
%-export([odds_and_evens/1]).
-compile(export_all).

sum(L) -> sum(L, 0).

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


for(Max, Max, F) -> [F(Max)];
for(I, Max, F) -> [F(I)|for(I+1, Max, F)].

qsort([]) -> [];
qsort([Pivot|T]) ->
        qsort([X || X<- T, X < Pivot])
        ++ [Pivot] ++
        qsort([X || X <- T, X >=Pivot]).

pythag(N) ->
    [ {A,B,C} || 
        A <- lists:seq(1,N),
        B <- lists:seq(1,N),
        C <- lists:seq(1,N),
        A+B+C =< N,
        A*A+B*B =:= C*C
    ].

perms([]) -> [[]];
perms(L) -> [[H|T] || H <- L, T <- perms(L--[H])].

%   filter(P, [H|T]) ->
%       case P(H) of
%           true -> [H|filter(P, T)];
%           false -> filter(P, T)
%       end;
%   filter(P, []) -> [].

odds_and_evens(L) ->
    Odds =  [X || X <- L, (X rem 2) =:= 1],
    Evens = [X || X <- L, (X rem 2) =:= 0],
    {Odds, Evens}.


odds_and_evens_acc(L) ->
    odds_and_evens_acc(L, [], []).

odds_and_evens_acc([H|T], Odds, Evens) ->
    case (H rem 2) of
        1 -> odds_and_evens_acc(T, [H|Odds], Evens);
        0 -> odds_and_evens_acc(T, Odds, [H|Evens])
    end;
odds_and_evens_acc([], Odds, Evens) ->
    {lists:reverse(Odds), lists:reverse(Evens)}.

on_exit(Pid, Fun) ->
    spawn(fun() ->
        process_flag(trap_exit, true),
        link(Pid),
        receive
            {'EXIT', Pid, Why} ->
                Fun(Why)
        end
    end).