Erlang snippets

do_monad.erl

-spec do(any(), [fun((...) -> any())]) -> any().
do(Arg, []) ->
    Arg;

do(Arg, [Fun | Funs]) ->
    case Fun(Arg) of
        {error, Data} ->
            Data;
        Data ->
            do(Data, Funs)
    end.

lhttpc_request_with_retry.erl

-spec lhttpc_request_with_retry(fun(() -> lhttpc:result()), integer()) -> lhttpc:result() | {error, no_attempts_left}.
lhttpc_request_with_retry(_, 0) ->
    {error, no_retries_left};
lhttpc_request_with_retry(RequestFun, AttemptsLeft) ->
    Res = RequestFun(),
    case Res of
        {ok, _} ->
            Res;
        {error, _} ->
            N = ?ATTEMPTS_TO_CONTACT - AttemptsLeft,
            timer:sleep(1000*N),
            lhttpc_request_with_retry(RequestFun, AttemptsLeft-1)
    end.

percentiles.erl

f(Percentiles).
Percentiles = fun(Numbers) ->
    Percentile = fun(List, Size, Perc) ->
        Element = round(Perc * Size),
        lists:nth(Element, List)
    end,
    Len = length(Numbers),
    Sorted = lists:sort(Numbers),
    [{trunc(Perc*100), Percentile(Sorted, Len, Perc)} ||
        Perc <- [0.50, 0.75, 0.90, 0.95, 0.99, 0.999]]
end.
%% Percentiles([3, 7, 2, 6.25, ...]).

test_helpers.erl

%% to prevent races
wait_until_finished(Pid) ->
    exit(Pid, shutdown),
    Ref = monitor(process, Pid),
    receive
        {'DOWN', Ref, process, Pid, _Reason} ->
            ok
    after 1000 ->
              error(exit_timeout)
    end.

time.erl

-spec get_timestamp() -> integer().
get_timestamp() ->
  {Mega, Sec, Micro} = os:timestamp(),
  (Mega*1000000 + Sec)*1000 + round(Micro/1000). % ms
  
iso8601({{Y,Mo,D}, {H,Mn,S}}) ->
  <<(integer_to_binary(Y))/binary, $-,
    ($0 + (Mo div 10)), ($0 + (Mo rem 10)), $-,
    ($0 + (D div 10)), ($0 + (D rem 10)), $T,
    ($0 + (H div 10)), ($0 + (H rem 10)), $:,
    ($0 + (Mn div 10)), ($0 + (Mn rem 10)), $:,
    ($0 + (S div 10)), ($0 + (S rem 10)), $Z>>.