Binary, List and Tuple Inequalities (Paradox?)

[Valentin Micic]

Thank you for jumping in. :-)
Am I alone in thinking that Barklund makes sense?

V/


> On 24 Nov 2019, at 01:51, Matthias Lang <matthias@REDACTED> wrote:
> 
> Jumping into a thread that's a few weeks old.
> 
> My first thought was to see what the 'Barklund' draft says:
> 
>   | An empty list precedes a cons ... and conses are ordered first by
>   | their heads, then by their tails. (Thus a longer list may preced a
>   | shorter list even though a shorter list tuple always precedes a
>   | longer tuple.) For example, [] < [a|2] <[a|b] < [a] < [a, a], [b].
>   |
>   | http://www.erlang.org/download/erl_spec47.ps.gz
> 
> So far no surprises, but then it says
> 
>   | Binaries are ordered first by their size, then according to their
>   | elements lexicographically. (That is, the same as the order
>   | between tuples of integers.
> 
> So I think the Barklund draft doesn't agree with the implementation.
> 
> I went back to OTP R8B. Even that doesn't agree with the Barklund draft:
> 
>  1> init:script_id().
>  {"OTP  APN 181 01","R8B"}    // I think R8B is from about 2002
>  2> <<0,0,1>> < <<1,0>>.
> true
> 
> I'm not sure if the Barklund draft never agreed with the implementation,
> or if the implementation changed some time before 2003.
> 
> Also, it seems that the current reference manual defines what happens
> for lists, but not binaries and bit strings:
> 
>  http://erlang.org/doc/reference_manual/expressions.html#term-comparisons
> 
> Matthias
> 
> ----------------------------------------------------------------------
> Date: 28. October 2019 From: Raimo Niskanen
> <raimo.niskanen@REDACTED> To erlang-questions@REDACTED Subject:
> Re: Binary, List and Tuple Inequalities (Paradox?)
> 
> 
>> I'd like to defend the current term order of lists, tuples and
>> binaries.
>> 
>> Lists are compared a'la string comparison, which avoids having to
>> traverse the whole list when comparing.  Binaries are compared as lists
>> since both are used for handling strings, and also to be compared like
>> memcmp does it.
>> 
>> Tuples are used for general complex terms.  They can be compared size
>> first whithout having to be fully traversed, as opposed to lists, which
>> is useful in other contexts.  You can thereby choose your data
>> structure to select comparision.
>> --
>> Raimo Niskanen
>>