[erlang-questions] Baffling lists

[Stu Bailey]

Thanks.  I actually wanted to reverse the list of lists lists:reverse(L4).
I did not know about "irregular lists".  Now I do.

Thanks again!

On Sun, Sep 21, 2014 at 8:00 AM, Dmytro Lytovchenko <
dmytro.lytovchenko@REDACTED> wrote:

> Oh and also its list of another list and 0 as tail element. You probably
> want to reverse first element of L4, like lists:reverse(hd(L4)).
>
> On Sun, Sep 21, 2014 at 4:51 PM, Dmytro Lytovchenko <
> dmytro.lytovchenko@REDACTED> wrote:
>
>> 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.
>>>
>>> _______________________________________________
>>> erlang-questions mailing list
>>> erlang-questions@REDACTED
>>> http://erlang.org/mailman/listinfo/erlang-questions
>>>
>>>
>>
>
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