[erlang-questions] Baffling lists

[Dmytro Lytovchenko]

It is irregular list, that is list which doesn't have [] as tail element,
and has 0 there instead. While its legal to have such a value, some list
handling functions will be waiting for [] as tail element thus they will be
confused.
Solution: don't have 0 there, or cut it away temporarily and append later
as X = [CutList | 0].

On Sun, Sep 21, 2014 at 4:46 PM, Stu Bailey <stu.bailey@REDACTED> wrote:

> I'm sure I'm missing something obvious, but here goes:
>
> What is going on here?  Is L4 a list?  If so, why can't I reverse it?
>
> 70> L4.
>
> [[<<"8">>,<<"7">>,<<"6">>,<<"5">>],
>
>  [<<"4">>,<<"3">>,<<"2">>,<<"1">>]|
>
>  0]
>
> 71> lists:reverse(L4).
>
> ** exception error: bad argument
>
>      in function  lists:reverse/2
>
>         called as lists:reverse(0,
>
>                                 [[<<"4">>,<<"3">>,<<"2">>,<<"1">>],
>
>                                  [<<"8">>,<<"7">>,<<"6">>,<<"5">>]])
>
>      in call from lists:reverse/1 (lists.erl, line 152)
>
> 72> [Head1|Rest1] = L4.
>
> [[<<"8">>,<<"7">>,<<"6">>,<<"5">>],
>
>  [<<"4">>,<<"3">>,<<"2">>,<<"1">>]|
>
>  0]
>
> 73> Rest1.
>
> [[<<"4">>,<<"3">>,<<"2">>,<<"1">>]|0]
>
> 74> lists:reverse(Rest1).
>
> ** exception error: no function clause matching
> lists:reverse([[<<"4">>,<<"3">>,<<"2">>,<<"1">>]|0]) (lists.erl, line 145)
>
> 75> [Head2|Rest2] = Rest1.
>
> [[<<"4">>,<<"3">>,<<"2">>,<<"1">>]|0]
>
> 76> Head2.
>
> [<<"4">>,<<"3">>,<<"2">>,<<"1">>]
>
> 77> Rest2.
>
> 0
>
> 78>
>
>
> In practice, the kind of structure demonstrated in L4 is being returned by
> a function from another library I'm trying to use, but I'm trying to
> understand what's going on in general.
>
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>
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