Seems like a worthy goal to me and I would say that you nailed it.

Thanks for the feedback everyone, I really appreciate it!

@sillypog
Great to see you again at the conf - thanks for the kind words! The trick I’ve found is to trip up a lot myself, and then just try to document everything that didn’t make any sense to me.

@JEG2
For sure, I’d love to have had another 30 minutes to talk so I could go deeper! I personally don’t have a ton of programming history prior to Elixir, so how macros work and especially the AST in general were difficult concepts for me to learn. I’ve heard some excellent talks that started just a couple levels above where my own knowledge was, so at the time I didn’t learn much because I couldn’t follow along.

So my top goal for this talk was that someone with very little background would walk out of the talk understanding 90% of what was covered, and that they could then watch any other Macro talks and be able to easily follow along by recognizing the same concepts. I also went long every time I did a run-through of the talk so I ended up cutting a couple of examples at the end that would’ve introduced a few more of concepts of Macros (e.g. I really wanted to do an example of __using__ but just didn’t have the time).

@axelson
As some others said, the reason for the 2-element tuple is to allow for the syntax of keyword lists, which I think might be important for the maintaining of do/else/etc blocks inside of the AST. I was planning to cover this in my original talk but had to cut it for time at the last minute. I’ve got the slide to prove it! There’s some additional info (though not a ton) in the Official Docs: Syntax Reference.

image.png514×550 64.8 KB

Also, could you add the elixirconf2017 tag to this post, thanks!

/Side note/

You can use a hash to auto-link to a tags page when in a post, e.g.: elixirconf2017

The reason that two-element tuples are special is so that keyword lists can be special. See the mailing list thread where José confirms it.

Zero and one item tuples could be special too, but I don’t think three item tuples could be. Since lists and atoms are literal I think there could be ambiguity between AST nodes and values. Something like {:x, [], []} might be representing x() or it might be the literal value {:x, [], []}.

So I think it could be either “all tuples are literals, except three item tuples”, or it could be “only two element tuples are literals”. I think having a single case where the rule doesn’t apply is more confusing than having a single case where the rule does apply. Though it could be that there is no ambiguity with three item tuples and I’m just overlooking something.

I actually really really really hate that things like 2-element tuples and literals are special cased, they lose their source positions and meta information. I wish everything, absolutely everything were 3-tuples.

Thankfully you can wrap literals in blocks to recover meta information, but you cannot do that to 2-tuples as things break I found out.