split_iolist

gistfile1.txt

1> c(s).
{ok,s}
2> s:s(1, [<<"abc">>, "def", ["ghi"] | <<"jkl">>]).
{<<"a">>,[<<"bc">>,"def",["ghi"]|<<"jkl">>]}
3> s:s(2, [<<"abc">>, "def", ["ghi"] | <<"jkl">>]).
{<<"ab">>,[<<"c">>,"def",["ghi"]|<<"jkl">>]}
4> s:s(3, [<<"abc">>, "def", ["ghi"] | <<"jkl">>]).
{<<"abc">>,["def",["ghi"]|<<"jkl">>]}
5> s:s(4, [<<"abc">>, "def", ["ghi"] | <<"jkl">>]).
{[<<"abc">>,100],["ef",["ghi"]|<<"jkl">>]}
6> s:s(5, [<<"abc">>, "def", ["ghi"] | <<"jkl">>]).
{[<<"abc">>,"de"],["f",["ghi"]|<<"jkl">>]}
7> s:s(6, [<<"abc">>, "def", ["ghi"] | <<"jkl">>]).
{[<<"abc">>,"def"],[["ghi"]|<<"jkl">>]}
8> s:s(7, [<<"abc">>, "def", ["ghi"] | <<"jkl">>]).
{[<<"abc">>,"def",103],[["hi"]|<<"jkl">>]}
9> s:s(8, [<<"abc">>, "def", ["ghi"] | <<"jkl">>]).
{[<<"abc">>,"def","gh"],[["i"]|<<"jkl">>]}
10> s:s(9, [<<"abc">>, "def", ["ghi"] | <<"jkl">>]).
{[<<"abc">>,"def",["ghi"]],<<"jkl">>}
11> s:s(10, [<<"abc">>, "def", ["ghi"] | <<"jkl">>]).
{[<<"abc">>,"def",["ghi"],<<"j">>],<<"kl">>}
12> s:s(11, [<<"abc">>, "def", ["ghi"] | <<"jkl">>]).
{[<<"abc">>,"def",["ghi"],<<"jk">>],<<"l">>}
13> s:s(12, [<<"abc">>, "def", ["ghi"] | <<"jkl">>]).
{[<<"abc">>,"def",["ghi"],<<"jkl">>],<<>>}
14> s:s(13, [<<"abc">>, "def", ["ghi"] | <<"jkl">>]).
{[<<"abc">>,"def",["ghi"],<<"jkl">>],<<>>}
15> s:s(0, [<<"abc">>, "def", ["ghi"] | <<"jkl">>]). 
{[],[<<"abc">>,"def",["ghi"]|<<"jkl">>]}
16> s:s(3, <<"abcde">>).                            
{<<"abc">>,<<"de">>}
17> s:s(5, <<"abcde">>).
{<<"abcde">>,<<>>}

s.erl

-module(s).
-compile(export_all).

s(Pos, Data) ->
    s(Pos, Data, []).

s(Pos, Post, [Acc]) when Pos =< 0 ->
    {Acc, Post};
s(Pos, Post, Acc) when Pos =< 0 ->
    {lists:reverse(Acc), Post};
s(Pos, [H | T], Acc) when is_integer(H) ->
    s(Pos - 1, T, [H | Acc]);
s(Pos, Data, Acc) when is_binary(Data) ->
    case byte_size(Data) > Pos of
        true  -> s(0, binary:part(Data, Pos, byte_size(Data) - Pos), [binary:part(Data, 0, Pos) | Acc]);
        false -> s(0, <<>>, [Data | Acc])
    end;
s(Pos, [H | T], Acc) ->
    HSize = iolist_size(H),
    case Pos >= HSize of
        true  -> s(Pos - HSize, T, [H | Acc]);
        false ->
            {Pre, Post} = s(Pos, H),
            s(0, [Post | T], [Pre | Acc])
    end.