-module(gleam@iterator).
-compile([no_auto_import, nowarn_unused_vars, nowarn_unused_function, nowarn_nomatch]).

-export([unfold/2, repeatedly/1, repeat/1, from_list/1, transform/3, fold/3, run/1, to_list/1, step/1, take/2, drop/2, map/2, map2/3, append/2, flatten/1, concat/1, flat_map/2, filter/2, filter_map/2, cycle/1, find/2, find_map/2, index/1, iterate/2, take_while/2, drop_while/2, scan/3, zip/2, chunk/2, sized_chunk/2, intersperse/2, any/2, all/2, group/2, reduce/2, last/1, empty/0, once/1, range/2, single/1, interleave/2, fold_until/3, try_fold/3, first/1, at/2, length/1, each/2, yield/2]).
-export_type([action/1, iterator/1, step/2, chunk/2, sized_chunk/1]).

-type action(BWK) :: stop | {continue, BWK, fun(() -> action(BWK))}.

-opaque iterator(BWL) :: {iterator, fun(() -> action(BWL))}.

-type step(BWM, BWN) :: {next, BWM, BWN} | done.

-type chunk(BWO, BWP) :: {another_by,
        list(BWO),
        BWP,
        BWO,
        fun(() -> action(BWO))} |
    {last_by, list(BWO)}.

-type sized_chunk(BWQ) :: {another, list(BWQ), fun(() -> action(BWQ))} |
    {last, list(BWQ)} |
    no_more.

-spec stop() -> action(any()).
stop() ->
    stop.

-spec do_unfold(BWT, fun((BWT) -> step(BWU, BWT))) -> fun(() -> action(BWU)).
do_unfold(Initial, F) ->
    fun() -> case F(Initial) of
            {next, X, Acc} ->
                {continue, X, do_unfold(Acc, F)};

            done ->
                stop
        end end.

-spec unfold(BWY, fun((BWY) -> step(BWZ, BWY))) -> iterator(BWZ).
unfold(Initial, F) ->
    _pipe = Initial,
    _pipe@1 = do_unfold(_pipe, F),
    {iterator, _pipe@1}.

-spec repeatedly(fun(() -> BXD)) -> iterator(BXD).
repeatedly(F) ->
    unfold(nil, fun(_) -> {next, F(), nil} end).

-spec repeat(BXF) -> iterator(BXF).
repeat(X) ->
    repeatedly(fun() -> X end).

-spec from_list(list(BXH)) -> iterator(BXH).
from_list(List) ->
    Yield = fun(Acc) -> case Acc of
            [] ->
                done;

            [Head | Tail] ->
                {next, Head, Tail}
        end end,
    unfold(List, Yield).

-spec do_transform(
    fun(() -> action(BXK)),
    BXM,
    fun((BXM, BXK) -> step(BXN, BXM))
) -> fun(() -> action(BXN)).
do_transform(Continuation, State, F) ->
    fun() -> case Continuation() of
            stop ->
                stop;

            {continue, El, Next} ->
                case F(State, El) of
                    done ->
                        stop;

                    {next, Yield, Next_state} ->
                        {continue, Yield, do_transform(Next, Next_state, F)}
                end
        end end.

-spec transform(iterator(BXR), BXT, fun((BXT, BXR) -> step(BXU, BXT))) -> iterator(BXU).
transform(Iterator, Initial, F) ->
    _pipe = do_transform(erlang:element(2, Iterator), Initial, F),
    {iterator, _pipe}.

-spec do_fold(fun(() -> action(BXY)), fun((BYA, BXY) -> BYA), BYA) -> BYA.
do_fold(Continuation, F, Accumulator) ->
    case Continuation() of
        {continue, Elem, Next} ->
            do_fold(Next, F, F(Accumulator, Elem));

        stop ->
            Accumulator
    end.

-spec fold(iterator(BYB), BYD, fun((BYD, BYB) -> BYD)) -> BYD.
fold(Iterator, Initial, F) ->
    _pipe = erlang:element(2, Iterator),
    do_fold(_pipe, F, Initial).

-spec run(iterator(any())) -> nil.
run(Iterator) ->
    fold(Iterator, nil, fun(_, _) -> nil end).

-spec to_list(iterator(BYG)) -> list(BYG).
to_list(Iterator) ->
    _pipe = Iterator,
    _pipe@1 = fold(_pipe, [], fun(Acc, E) -> [E | Acc] end),
    lists:reverse(_pipe@1).

-spec step(iterator(BYJ)) -> step(BYJ, iterator(BYJ)).
step(Iterator) ->
    case (erlang:element(2, Iterator))() of
        stop ->
            done;

        {continue, E, A} ->
            {next, E, {iterator, A}}
    end.

-spec do_take(fun(() -> action(BYO)), integer()) -> fun(() -> action(BYO)).
do_take(Continuation, Desired) ->
    fun() -> case Desired > 0 of
            false ->
                stop;

            true ->
                case Continuation() of
                    stop ->
                        stop;

                    {continue, E, Next} ->
                        {continue, E, do_take(Next, Desired - 1)}
                end
        end end.

-spec take(iterator(BYR), integer()) -> iterator(BYR).
take(Iterator, Desired) ->
    _pipe = erlang:element(2, Iterator),
    _pipe@1 = do_take(_pipe, Desired),
    {iterator, _pipe@1}.

-spec do_drop(fun(() -> action(BYU)), integer()) -> action(BYU).
do_drop(Continuation, Desired) ->
    case Continuation() of
        stop ->
            stop;

        {continue, E, Next} ->
            case Desired > 0 of
                true ->
                    do_drop(Next, Desired - 1);

                false ->
                    {continue, E, Next}
            end
    end.

-spec drop(iterator(BYX), integer()) -> iterator(BYX).
drop(Iterator, Desired) ->
    _pipe = fun() -> do_drop(erlang:element(2, Iterator), Desired) end,
    {iterator, _pipe}.

-spec do_map(fun(() -> action(BZA)), fun((BZA) -> BZC)) -> fun(() -> action(BZC)).
do_map(Continuation, F) ->
    fun() -> case Continuation() of
            stop ->
                stop;

            {continue, E, Continuation@1} ->
                {continue, F(E), do_map(Continuation@1, F)}
        end end.

-spec map(iterator(BZE), fun((BZE) -> BZG)) -> iterator(BZG).
map(Iterator, F) ->
    _pipe = erlang:element(2, Iterator),
    _pipe@1 = do_map(_pipe, F),
    {iterator, _pipe@1}.

-spec do_map2(
    fun(() -> action(BZI)),
    fun(() -> action(BZK)),
    fun((BZI, BZK) -> BZM)
) -> fun(() -> action(BZM)).
do_map2(Continuation1, Continuation2, Fun) ->
    fun() -> case Continuation1() of
            stop ->
                stop;

            {continue, A, Next_a} ->
                case Continuation2() of
                    stop ->
                        stop;

                    {continue, B, Next_b} ->
                        {continue, Fun(A, B), do_map2(Next_a, Next_b, Fun)}
                end
        end end.

-spec map2(iterator(BZO), iterator(BZQ), fun((BZO, BZQ) -> BZS)) -> iterator(BZS).
map2(Iterator1, Iterator2, Fun) ->
    _pipe = do_map2(
        erlang:element(2, Iterator1),
        erlang:element(2, Iterator2),
        Fun
    ),
    {iterator, _pipe}.

-spec do_append(fun(() -> action(BZU)), fun(() -> action(BZU))) -> action(BZU).
do_append(First, Second) ->
    case First() of
        {continue, E, First@1} ->
            {continue, E, fun() -> do_append(First@1, Second) end};

        stop ->
            Second()
    end.

-spec append(iterator(BZY), iterator(BZY)) -> iterator(BZY).
append(First, Second) ->
    _pipe = fun() ->
        do_append(erlang:element(2, First), erlang:element(2, Second))
    end,
    {iterator, _pipe}.

-spec do_flatten(fun(() -> action(iterator(CAC)))) -> action(CAC).
do_flatten(Flattened) ->
    case Flattened() of
        stop ->
            stop;

        {continue, It, Next_iterator} ->
            do_append(
                erlang:element(2, It),
                fun() -> do_flatten(Next_iterator) end
            )
    end.

-spec flatten(iterator(iterator(CAG))) -> iterator(CAG).
flatten(Iterator) ->
    _pipe = fun() -> do_flatten(erlang:element(2, Iterator)) end,
    {iterator, _pipe}.

-spec concat(list(iterator(CAK))) -> iterator(CAK).
concat(Iterators) ->
    flatten(from_list(Iterators)).

-spec flat_map(iterator(CAO), fun((CAO) -> iterator(CAQ))) -> iterator(CAQ).
flat_map(Iterator, F) ->
    _pipe = Iterator,
    _pipe@1 = map(_pipe, F),
    flatten(_pipe@1).

-spec do_filter(fun(() -> action(CAT)), fun((CAT) -> boolean())) -> action(CAT).
do_filter(Continuation, Predicate) ->
    case Continuation() of
        stop ->
            stop;

        {continue, E, Iterator} ->
            case Predicate(E) of
                true ->
                    {continue, E, fun() -> do_filter(Iterator, Predicate) end};

                false ->
                    do_filter(Iterator, Predicate)
            end
    end.

-spec filter(iterator(CAW), fun((CAW) -> boolean())) -> iterator(CAW).
filter(Iterator, Predicate) ->
    _pipe = fun() -> do_filter(erlang:element(2, Iterator), Predicate) end,
    {iterator, _pipe}.

-spec do_filter_map(
    fun(() -> action(CAZ)),
    fun((CAZ) -> {ok, CBB} | {error, any()})
) -> action(CBB).
do_filter_map(Continuation, F) ->
    case Continuation() of
        stop ->
            stop;

        {continue, E, Next} ->
            case F(E) of
                {ok, E@1} ->
                    {continue, E@1, fun() -> do_filter_map(Next, F) end};

                {error, _} ->
                    do_filter_map(Next, F)
            end
    end.

-spec filter_map(iterator(CBG), fun((CBG) -> {ok, CBI} | {error, any()})) -> iterator(CBI).
filter_map(Iterator, F) ->
    _pipe = fun() -> do_filter_map(erlang:element(2, Iterator), F) end,
    {iterator, _pipe}.

-spec cycle(iterator(CBN)) -> iterator(CBN).
cycle(Iterator) ->
    _pipe = repeat(Iterator),
    flatten(_pipe).

-spec do_find(fun(() -> action(CBR)), fun((CBR) -> boolean())) -> {ok, CBR} |
    {error, nil}.
do_find(Continuation, F) ->
    case Continuation() of
        stop ->
            {error, nil};

        {continue, E, Next} ->
            case F(E) of
                true ->
                    {ok, E};

                false ->
                    do_find(Next, F)
            end
    end.

-spec find(iterator(CBV), fun((CBV) -> boolean())) -> {ok, CBV} | {error, nil}.
find(Haystack, Is_desired) ->
    _pipe = erlang:element(2, Haystack),
    do_find(_pipe, Is_desired).

-spec do_find_map(
    fun(() -> action(CBZ)),
    fun((CBZ) -> {ok, CCB} | {error, any()})
) -> {ok, CCB} | {error, nil}.
do_find_map(Continuation, F) ->
    case Continuation() of
        stop ->
            {error, nil};

        {continue, E, Next} ->
            case F(E) of
                {ok, E@1} ->
                    {ok, E@1};

                {error, _} ->
                    do_find_map(Next, F)
            end
    end.

-spec find_map(iterator(CCH), fun((CCH) -> {ok, CCJ} | {error, any()})) -> {ok,
        CCJ} |
    {error, nil}.
find_map(Haystack, Is_desired) ->
    _pipe = erlang:element(2, Haystack),
    do_find_map(_pipe, Is_desired).

-spec do_index(fun(() -> action(CCP)), integer()) -> fun(() -> action({CCP,
    integer()})).
do_index(Continuation, Next) ->
    fun() -> case Continuation() of
            stop ->
                stop;

            {continue, E, Continuation@1} ->
                {continue, {E, Next}, do_index(Continuation@1, Next + 1)}
        end end.

-spec index(iterator(CCS)) -> iterator({CCS, integer()}).
index(Iterator) ->
    _pipe = erlang:element(2, Iterator),
    _pipe@1 = do_index(_pipe, 0),
    {iterator, _pipe@1}.

-spec iterate(CCV, fun((CCV) -> CCV)) -> iterator(CCV).
iterate(Initial, F) ->
    unfold(Initial, fun(Element) -> {next, Element, F(Element)} end).

-spec do_take_while(fun(() -> action(CCX)), fun((CCX) -> boolean())) -> fun(() -> action(CCX)).
do_take_while(Continuation, Predicate) ->
    fun() -> case Continuation() of
            stop ->
                stop;

            {continue, E, Next} ->
                case Predicate(E) of
                    false ->
                        stop;

                    true ->
                        {continue, E, do_take_while(Next, Predicate)}
                end
        end end.

-spec take_while(iterator(CDA), fun((CDA) -> boolean())) -> iterator(CDA).
take_while(Iterator, Predicate) ->
    _pipe = erlang:element(2, Iterator),
    _pipe@1 = do_take_while(_pipe, Predicate),
    {iterator, _pipe@1}.

-spec do_drop_while(fun(() -> action(CDD)), fun((CDD) -> boolean())) -> action(CDD).
do_drop_while(Continuation, Predicate) ->
    case Continuation() of
        stop ->
            stop;

        {continue, E, Next} ->
            case Predicate(E) of
                false ->
                    {continue, E, Next};

                true ->
                    do_drop_while(Next, Predicate)
            end
    end.

-spec drop_while(iterator(CDG), fun((CDG) -> boolean())) -> iterator(CDG).
drop_while(Iterator, Predicate) ->
    _pipe = fun() -> do_drop_while(erlang:element(2, Iterator), Predicate) end,
    {iterator, _pipe}.

-spec do_scan(fun(() -> action(CDJ)), fun((CDL, CDJ) -> CDL), CDL) -> fun(() -> action(CDL)).
do_scan(Continuation, F, Accumulator) ->
    fun() -> case Continuation() of
            stop ->
                stop;

            {continue, El, Next} ->
                Accumulated = F(Accumulator, El),
                {continue, Accumulated, do_scan(Next, F, Accumulated)}
        end end.

-spec scan(iterator(CDN), CDP, fun((CDP, CDN) -> CDP)) -> iterator(CDP).
scan(Iterator, Initial, F) ->
    _pipe = erlang:element(2, Iterator),
    _pipe@1 = do_scan(_pipe, F, Initial),
    {iterator, _pipe@1}.

-spec do_zip(fun(() -> action(CDR)), fun(() -> action(CDT))) -> fun(() -> action({CDR,
    CDT})).
do_zip(Left, Right) ->
    fun() -> case Left() of
            stop ->
                stop;

            {continue, El_left, Next_left} ->
                case Right() of
                    stop ->
                        stop;

                    {continue, El_right, Next_right} ->
                        {continue,
                            {El_left, El_right},
                            do_zip(Next_left, Next_right)}
                end
        end end.

-spec zip(iterator(CDW), iterator(CDY)) -> iterator({CDW, CDY}).
zip(Left, Right) ->
    _pipe = do_zip(erlang:element(2, Left), erlang:element(2, Right)),
    {iterator, _pipe}.

-spec next_chunk(fun(() -> action(CEB)), fun((CEB) -> CED), CED, list(CEB)) -> chunk(CEB, CED).
next_chunk(Continuation, F, Previous_key, Current_chunk) ->
    case Continuation() of
        stop ->
            {last_by, lists:reverse(Current_chunk)};

        {continue, E, Next} ->
            Key = F(E),
            case Key =:= Previous_key of
                true ->
                    next_chunk(Next, F, Key, [E | Current_chunk]);

                false ->
                    {another_by, lists:reverse(Current_chunk), Key, E, Next}
            end
    end.

-spec do_chunk(fun(() -> action(CEH)), fun((CEH) -> CEJ), CEJ, CEH) -> action(list(CEH)).
do_chunk(Continuation, F, Previous_key, Previous_element) ->
    case next_chunk(Continuation, F, Previous_key, [Previous_element]) of
        {last_by, Chunk} ->
            {continue, Chunk, fun stop/0};

        {another_by, Chunk@1, Key, El, Next} ->
            {continue, Chunk@1, fun() -> do_chunk(Next, F, Key, El) end}
    end.

-spec chunk(iterator(CEM), fun((CEM) -> any())) -> iterator(list(CEM)).
chunk(Iterator, F) ->
    _pipe = fun() -> case (erlang:element(2, Iterator))() of
            stop ->
                stop;

            {continue, E, Next} ->
                do_chunk(Next, F, F(E), E)
        end end,
    {iterator, _pipe}.

-spec next_sized_chunk(fun(() -> action(CER)), integer(), list(CER)) -> sized_chunk(CER).
next_sized_chunk(Continuation, Left, Current_chunk) ->
    case Continuation() of
        stop ->
            case Current_chunk of
                [] ->
                    no_more;

                Remaining ->
                    {last, lists:reverse(Remaining)}
            end;

        {continue, E, Next} ->
            Chunk = [E | Current_chunk],
            case Left > 1 of
                false ->
                    {another, lists:reverse(Chunk), Next};

                true ->
                    next_sized_chunk(Next, Left - 1, Chunk)
            end
    end.

-spec do_sized_chunk(fun(() -> action(CEV)), integer()) -> fun(() -> action(list(CEV))).
do_sized_chunk(Continuation, Count) ->
    fun() -> case next_sized_chunk(Continuation, Count, []) of
            no_more ->
                stop;

            {last, Chunk} ->
                {continue, Chunk, fun stop/0};

            {another, Chunk@1, Next_element} ->
                {continue, Chunk@1, do_sized_chunk(Next_element, Count)}
        end end.

-spec sized_chunk(iterator(CEZ), integer()) -> iterator(list(CEZ)).
sized_chunk(Iterator, Count) ->
    _pipe = erlang:element(2, Iterator),
    _pipe@1 = do_sized_chunk(_pipe, Count),
    {iterator, _pipe@1}.

-spec do_intersperse(fun(() -> action(CFD)), CFD) -> action(CFD).
do_intersperse(Continuation, Separator) ->
    case Continuation() of
        stop ->
            stop;

        {continue, E, Next} ->
            Next_interspersed = fun() -> do_intersperse(Next, Separator) end,
            {continue, Separator, fun() -> {continue, E, Next_interspersed} end}
    end.

-spec intersperse(iterator(CFG), CFG) -> iterator(CFG).
intersperse(Iterator, Elem) ->
    _pipe = fun() -> case (erlang:element(2, Iterator))() of
            stop ->
                stop;

            {continue, E, Next} ->
                {continue, E, fun() -> do_intersperse(Next, Elem) end}
        end end,
    {iterator, _pipe}.

-spec do_any(fun(() -> action(CFJ)), fun((CFJ) -> boolean())) -> boolean().
do_any(Continuation, Predicate) ->
    case Continuation() of
        stop ->
            false;

        {continue, E, Next} ->
            case Predicate(E) of
                true ->
                    true;

                false ->
                    do_any(Next, Predicate)
            end
    end.

-spec any(iterator(CFL), fun((CFL) -> boolean())) -> boolean().
any(Iterator, Predicate) ->
    _pipe = erlang:element(2, Iterator),
    do_any(_pipe, Predicate).

-spec do_all(fun(() -> action(CFN)), fun((CFN) -> boolean())) -> boolean().
do_all(Continuation, Predicate) ->
    case Continuation() of
        stop ->
            true;

        {continue, E, Next} ->
            case Predicate(E) of
                true ->
                    do_all(Next, Predicate);

                false ->
                    false
            end
    end.

-spec all(iterator(CFP), fun((CFP) -> boolean())) -> boolean().
all(Iterator, Predicate) ->
    _pipe = erlang:element(2, Iterator),
    do_all(_pipe, Predicate).

-spec update_group_with(CFR) -> fun((gleam@option:option(list(CFR))) -> list(CFR)).
update_group_with(El) ->
    fun(Maybe_group) -> case Maybe_group of
            {some, Group} ->
                [El | Group];

            none ->
                [El]
        end end.

-spec group_updater(fun((CFV) -> CFW)) -> fun((gleam@dict:dict(CFW, list(CFV)), CFV) -> gleam@dict:dict(CFW, list(CFV))).
group_updater(F) ->
    fun(Groups, Elem) -> _pipe = Groups,
        gleam@dict:update(_pipe, F(Elem), update_group_with(Elem)) end.

-spec group(iterator(CGD), fun((CGD) -> CGF)) -> gleam@dict:dict(CGF, list(CGD)).
group(Iterator, Key) ->
    _pipe = Iterator,
    _pipe@1 = fold(_pipe, gleam@dict:new(), group_updater(Key)),
    gleam@dict:map_values(_pipe@1, fun(_, Group) -> lists:reverse(Group) end).

-spec reduce(iterator(CGJ), fun((CGJ, CGJ) -> CGJ)) -> {ok, CGJ} | {error, nil}.
reduce(Iterator, F) ->
    case (erlang:element(2, Iterator))() of
        stop ->
            {error, nil};

        {continue, E, Next} ->
            _pipe = do_fold(Next, F, E),
            {ok, _pipe}
    end.

-spec last(iterator(CGN)) -> {ok, CGN} | {error, nil}.
last(Iterator) ->
    _pipe = Iterator,
    reduce(_pipe, fun(_, Elem) -> Elem end).

-spec empty() -> iterator(any()).
empty() ->
    {iterator, fun stop/0}.

-spec once(fun(() -> CGT)) -> iterator(CGT).
once(F) ->
    _pipe = fun() -> {continue, F(), fun stop/0} end,
    {iterator, _pipe}.

-spec range(integer(), integer()) -> iterator(integer()).
range(Start, Stop) ->
    case gleam@int:compare(Start, Stop) of
        eq ->
            once(fun() -> Start end);

        gt ->
            unfold(Start, fun(Current) -> case Current < Stop of
                        false ->
                            {next, Current, Current - 1};

                        true ->
                            done
                    end end);

        lt ->
            unfold(Start, fun(Current@1) -> case Current@1 > Stop of
                        false ->
                            {next, Current@1, Current@1 + 1};

                        true ->
                            done
                    end end)
    end.

-spec single(CGV) -> iterator(CGV).
single(Elem) ->
    once(fun() -> Elem end).

-spec do_interleave(fun(() -> action(CGX)), fun(() -> action(CGX))) -> action(CGX).
do_interleave(Current, Next) ->
    case Current() of
        stop ->
            Next();

        {continue, E, Next_other} ->
            {continue, E, fun() -> do_interleave(Next, Next_other) end}
    end.

-spec interleave(iterator(CHB), iterator(CHB)) -> iterator(CHB).
interleave(Left, Right) ->
    _pipe = fun() ->
        do_interleave(erlang:element(2, Left), erlang:element(2, Right))
    end,
    {iterator, _pipe}.

-spec do_fold_until(
    fun(() -> action(CHF)),
    fun((CHH, CHF) -> gleam@list:continue_or_stop(CHH)),
    CHH
) -> CHH.
do_fold_until(Continuation, F, Accumulator) ->
    case Continuation() of
        stop ->
            Accumulator;

        {continue, Elem, Next} ->
            case F(Accumulator, Elem) of
                {continue, Accumulator@1} ->
                    do_fold_until(Next, F, Accumulator@1);

                {stop, Accumulator@2} ->
                    Accumulator@2
            end
    end.

-spec fold_until(
    iterator(CHJ),
    CHL,
    fun((CHL, CHJ) -> gleam@list:continue_or_stop(CHL))
) -> CHL.
fold_until(Iterator, Initial, F) ->
    _pipe = erlang:element(2, Iterator),
    do_fold_until(_pipe, F, Initial).

-spec do_try_fold(
    fun(() -> action(CHN)),
    fun((CHP, CHN) -> {ok, CHP} | {error, CHQ}),
    CHP
) -> {ok, CHP} | {error, CHQ}.
do_try_fold(Continuation, F, Accumulator) ->
    case Continuation() of
        stop ->
            {ok, Accumulator};

        {continue, Elem, Next} ->
            gleam@result:'try'(
                F(Accumulator, Elem),
                fun(Accumulator@1) -> do_try_fold(Next, F, Accumulator@1) end
            )
    end.

-spec try_fold(iterator(CHV), CHX, fun((CHX, CHV) -> {ok, CHX} | {error, CHY})) -> {ok,
        CHX} |
    {error, CHY}.
try_fold(Iterator, Initial, F) ->
    _pipe = erlang:element(2, Iterator),
    do_try_fold(_pipe, F, Initial).

-spec first(iterator(CID)) -> {ok, CID} | {error, nil}.
first(Iterator) ->
    case (erlang:element(2, Iterator))() of
        stop ->
            {error, nil};

        {continue, E, _} ->
            {ok, E}
    end.

-spec at(iterator(CIH), integer()) -> {ok, CIH} | {error, nil}.
at(Iterator, Index) ->
    _pipe = Iterator,
    _pipe@1 = drop(_pipe, Index),
    first(_pipe@1).

-spec do_length(fun(() -> action(any())), integer()) -> integer().
do_length(Continuation, Length) ->
    case Continuation() of
        stop ->
            Length;

        {continue, _, Next} ->
            do_length(Next, Length + 1)
    end.

-spec length(iterator(any())) -> integer().
length(Iterator) ->
    _pipe = erlang:element(2, Iterator),
    do_length(_pipe, 0).

-spec each(iterator(CIP), fun((CIP) -> any())) -> nil.
each(Iterator, F) ->
    _pipe = Iterator,
    _pipe@1 = map(_pipe, F),
    run(_pipe@1).

-spec yield(CIS, fun(() -> iterator(CIS))) -> iterator(CIS).
yield(Element, Next) ->
    {iterator, fun() -> {continue, Element, erlang:element(2, Next())} end}.