Sorry, I wasn't asking a question. I was making a proposal as it says in
the title. Maybe the body of my message didn't convey that well or are you
saying that proposals to change the language shouldn't be made on this
mailing list?
You're right that the current parsing of that statement does not make
sense. I was suggesting instead of it being parsed like `[x: 1, y: (2 | [z:
3])]` it was parsed like `[{:x, 1}, {:y, 2} | [z: 3]]`.
It is definitely true you can use the list concatenation operator to do
what I'm suggesting, but that can have performance implications if the list
on the left is large. The cons operator on the other hand is a constant
time operation.
This was something I noticed that seemed inconsistent to me. If there's a
very good reason not to support it, that's fine.
Allen Madsen
http://www.allenmadsen.com
On Thu, Sep 14, 2017 at 12:52 PM, Alexei Sholik <[email protected]>
wrote:
> Questions like this should be asked on the Elixir Forum.
>
> The problem with the expression `[x: 1, y: 2 | [z: 3]]` is that it is
> parsed as `[x: 1, y: (2 | [z: 3])]`. As you may guess, the subexpression `2
> | [z: 3]` does not make sense.
>
> There's actually a working way to build the keyword list you want: [x: 1,
> y: 2] ++ [z: 3].
>
> On Wed, Sep 13, 2017 at 3:56 PM, Allen Madsen <[email protected]> wrote:
>
>> Yesterday I wrote code like the following:
>>
>> [x: 1, y: 2 | [z: 3]]
>>
>> I was really surprised when it didn't compile:
>>
>> ** (CompileError) iex:1: undefined function |/2
>> (stdlib) lists.erl:1354: :lists.mapfoldl/3
>> (stdlib) lists.erl:1355: :lists.mapfoldl/3
>>
>> The non-shorthand version works fine.
>>
>> [{:x, 1}, {:y, 2} | [z: 3]]
>> #=> [x: 1, y: 2, z: 3]
>>
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