Re: [RFC] Syntax for appending elements to arrays

[Jose E. Marchesi]

> On Thu, Nov 26, 2020 at 09:34:52AM +0100, Jose E. Marchesi wrote:
>> 
>> I just realized 2) is unfortunately ambiguous with the existing
>> array-concatenation operation.  If you have:
>> 
>>   var a = [[1,2],[3,4]];
>> 
>> And you do:
>> 
>>   a += [5,6];
>> 
>> Are you actually trying to concatenate the arrays [[1,2],[3,4]] and
>> [5,6], in which case you want a syntax error, or
>> 
>> Are you actually tring to append an element [5,6]?
>> 
>> If no one comes with some sane syntax for this, we will have to resort
>> to the usual notation:
>> 
>>   a.push ([5,6]) or,
>>   a.append ([5,6])
>> 
>> But I would really want to avoid that if possible..
>> 
>> No more ideas, anyone?
>> 
>
>
> Despite the fact I may miss something obvious, I try to explain my approach
> to deal with`lhs += rhs` in pseudo-code:
>
>     if (type (lhs) == ARRAY)
>     {
>         if (arr_elem_type (lhs) == type (rhs))
>           arr_append_elem (lhs, rhs);
>       else if (type (rhs) == ARRAY &&
>                arr_elem_type (lhs) == arr_elem_type (rhs))
>           arr_concat (lhs, rhs);
>       else
>           error ();
>     }
>     /* ... */

Yes, I see that logic.  But I think it is way too complicated and can
easily lead to confusion.

> So, here we will have:
>
> ```poke
> var a = [[1,2],[3,4]];
>
> a += [5,6];
> assert (a == [[1,2],[3,4],[5,6]]);
> ```
> This approach is also backward-compatible with current Poke codes.
>
> But if this is too complicated to implement or understand, introducing an
> `append` function is not that bad.
> Also having an `extend` function is desirable.
>
> ```poke
> a = [1,2,3];
> b = [4,5];
>
> a.extend(b);
> assert (a == [1,2,3,4,5]);
> ```

If we go this way, I would take inspiration from Icon (once again) and
have operations:

([1,2,3]).push (4)

  - Side-effect: [1,2,3] -> [4,1,2,3]
  - Evals to [4,2,3,4]
  
([1,2,3]).pop

  - Side-effect: [1,2,3] -> [2,3]
  - Evals to 1.

([1,2,3]).put (4)

  - Side-effect: [1,2,3] -> [1,2,3,4]
  - Evals to [1,2,3,4]

([1,2,3]).pull

  - Side-effect: [1,2,3] -> [1,2]
  - Evals to 3