Fully document array-like literal initializers

[pao]

The documentation on the Punctuation page isn't really useful if you're trying to specify a particular array structure, unless you already know MATLAB (and even then there are important differences). The literal syntaxes using [], {}, and (,) should be separated out into their own thing. Not sure what part of the manual is best. Examples should be included as well.

[kmsquire]

I cringe when I see the documentation for the special concatenation syntax (which was already there). I understand its usefulness in linear algebra... and I've been trying to justify it (unsuccessfully) to a new Julia user who wasn't doing linear algebra and couldn't figure out why he couldn't create hierarchical array structures (ala JSON).

[StefanKarpinski]

I agree it's a bad situation for general programming. I'm in favor of using |A B| for concatenation – curlies just aren't associated with block matrix syntax. They could get used for dicts and set literals(!).

[JeffBezanson]

I really regret imitating that other language's block matrix syntax.

The primary syntax should be for constructing arrays from elements, and supporting full N-d so that all arrays have a standard notation.

There might be some way to combine dict and set literals (e.g. write a dict as a set of tuples?), but I suspect we'll just have to forgo set literals.

We might be able to keep using spaces and semicolons to concatenate ([a b], [a; b], [a;]). You'd have to write [1:n;] to expand a range but we'd just have to live with that.

Another option is to leave [ ] alone, and reclaim { } for the new non-concatenating N-d array syntax.

[johnmyleswhite]

This is a slightly ridiculous proposal, but what about repetition of commas to indicate dimension?

• {1, 2, 3} is Array(Int, 3).
• {1,, 2,, 3} is Array(Int, 1, 3)
• {1,,, 2,,, 3} is Array(Int, 1, 1, 3)
• ...
• {1, 2,, 3, 4} is Array(Int, 2, 2) and equal to our current [1 3; 2 4].

[pao]

Nice thought, but it breaks down when you use this for 2D (which we do). With that proposal and multiline, you end up with:

> { 1, 2 ,,
    3, 4}

2x2 Array{Int64, 2}:
 1  3
 2  4

You have to mentally transpose the layout. I like that it can extend to higher dimensions though.