[erlang-bugs] Maps equality failure / Maps merge failure

[Kostis Sagonas]

On 03/24/2015 11:00 PM, Jesper Louis Andersen wrote:
> Erlang/OTP 17 [erts-6.3.1] [source-a1520d8] [64-bit] [smp:8:8]
> [async-threads:10] [hipe] [kernel-poll:false]
>
> Eshell V6.3.1  (abort with ^G)
> 1> L = [{-1,0},{0.0,0},{0,0},{1,0}].
> [{-1,0},{0.0,0},{0,0},{1,0}]
> 2> lists:sort(L).
> [{-1,0},{0.0,0},{0,0},{1,0}]
> 3> lists:sort(maps:to_list(maps:from_list(L))).
> [{-1,0},{0,0},{0.0,0},{1,0}]
> 4> v(2) =:= v(3).
> false
> 5> maps:to_list(maps:from_list(L)).
> [{-1,0},{0,0},{1,0},{0.0,0}]
>
> In other words, factoring L through a map makes the comparison and the
> sort go wrong.

The above may seem a bit weird at first but is not at all strange given 
that lists:sort/1 does not sort according to the (total) term order:

   Eshell V6.3.1  (abort with ^G)
   1> lists:sort([0, 0.0]).
   [0,0.0]
   2> lists:sort([0.0, 0]).
   [0.0,0]


and maps:to_list/1's manual page reads:

   to_list(Map) -> [{Key, Value}]

     Types:
       Map = #{}
       Key = Value = term()

   The fuction returns a list of pairs representing the key-value
   associations of Map, where the pairs, [{K1,V1}, ..., {Kn,Vn}], are
   returned in arbitrary order.


Kostis

PS. However, the manual has a typo: "fuction" should read "function" :)