Rename macro_rules! to macro!

[bluss]

Use a shorter and easier to understand name for this oft-used syntax extension.

[glaebhoerl]

What about define! to parallel C?

[Kimundi]

@glehel I think we don't want people to think that our macros work like C macros, so we might not wanna mirror that name.

[bluss]

To implement this change, is it possible to just add the macro syntax extension twice, once under the new name, and then migrate all instances after a snapshot?

[Aatch]

@blake2-ppc it should be possible to do that, basically just register another syntax extension that goes to the same code.

Also, I'm nominating this for backwards compatible.

[bstrie]

I believe that @paulstansifer and/or @jbclements specifically favored the macro_rules name for similarity with Scheme's syntax-rules construct. I personally wouldn't be opposed to the shorter name.

[bstrie]

Though perhaps we could find a middle ground and rename macro_rules! to syntax!. This has the bonus effect of no longer misleading C programmers into thinking that our macros are textual, but it does risk confusion with syntax extensions.

[paulstansifer]

Have we thought about what we will name the procedural-macro-generating construct, when that is implemented? If we have multiple ways of defining macros, it seems like it would be weird for only one of them to be called macro.

[jbclements]

I have no dog in this fight; I'm not a strong defender of macro_rules!.

[bstrie]

@paulstansifer What is this procedural-macro-generating construct you speak of?

[paulstansifer]

@bstrie It doesn't exist, but the prevailing mood (as I understand it) is that it should exist, eventually.

[catamorphism]

Leaving this up for debate. Macros are not in scope for 1.0, so de-milestoning

[nikomatsakis]

I prefer the name macro!()

[huonw]

Triage: as @catamorphism says, no change, but not an 1.0 concern due to feature-gating.

I do agree with @paulstansifer though: calling this macro when there are possibilities of other macro-generating constructs (especially now that we have loadable syntax extensions: anyone can write a macro-making macro now).