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The html5ever parser source [1] is remarkably easy to read, since it uses the Rust macro system to represent the state transitions declaratively. It also uses p

The html5ever parser source [1] is remarkably easy to read, since it uses the Rust macro system to represent the state transitions declaratively. It also uses pattern matching to nice effect. [1]: https://github.com/servo/html5ever/blob/master/html5ever/src/tokenizer/mod.rs https://github.com/servo/html5ever/blob/master/html5ever/src...

SwellJoe 9y ago
I would hope it would be nice to read since one could argue Rust was designed for the purpose of building Servo. So, if you can't implement Servo nicely in Rust, it'd be a pretty bad design.
- kibwen 9y ago
  I think you've mistaken what pcwalton was trying to say. This library is interesting because (via macros) it creates a DSL that attempts to emulate how the HTML 5 spec is written, in order to more easily verify the correctness of the implementation. Note that, by dint of much of HTML being an accident of history, the HTML 5 spec is somewhat imposing; it's not going to be a cakewalk in any language, and at the same time it's bespoke enough that it would be silly to design your language to cater to the needs of the HTML 5 spec in particular. The fact that Rust can create DSLs via macros does help here, though I wouldn't recommend this approach for anything other than a similarly extreme case. In fact I'd say this library has the most extensive macro use of any production Rust code I've ever seen, it's quite atypical as far as Rust code goes.
- vertex-four 9y ago
  If Rust were solely designed for the purpose of building Servo, we'd have OO - Servo quite badly wants it for the DOM - and a whole bunch of other one-off features. In practice, Rust is a language built for systems development in general with Servo having been an early testbed to make sure it's going in the right direction.
ucarion 9y ago
It might be worth linking to the talk that discusses html5ever's use of macros? I'm having trouble finding it.
- Ygg2 9y ago
  Here are the slides: https://kmcallister.github.io/talks/rust/2014-rust-macros/slides.html https://kmcallister.github.io/talks/rust/2014-rust-macros/sl... Here is the video (starts around 20min): https://air.mozilla.org/bay-area-rust-meetup-november-2014/ https://air.mozilla.org/bay-area-rust-meetup-november-2014/
Ygg2 9y ago
Perhaps a better comparisson is this: https://github.com/servo/html5ever/blob/master/html5ever/src/tokenizer/mod.rs#L683 https://github.com/servo/html5ever/blob/master/html5ever/src... https://html.spec.whatwg.org/multipage/parsing.html#data-state https://html.spec.whatwg.org/multipage/parsing.html#data-sta... Where spec: U+0000 NULL -> This is an unexpected-null-character parse error. Emit the current input character as a character token. translates into: FromSet('\0') => go!(self: error; emit '\0'), If you ignore the FromSet which is used for small set of characters, and `go!` which is a macro, you get something akin to: '\0' => emit_error; emit '\0'

SwellJoe 9y ago

I would hope it would be nice to read since one could argue Rust was designed for the purpose of building Servo. So, if you can't implement Servo nicely in Rust, it'd be a pretty bad design.

kibwen 9y ago
I think you've mistaken what pcwalton was trying to say. This library is interesting because (via macros) it creates a DSL that attempts to emulate how the HTML 5 spec is written, in order to more easily verify the correctness of the implementation. Note that, by dint of much of HTML being an accident of history, the HTML 5 spec is somewhat imposing; it's not going to be a cakewalk in any language, and at the same time it's bespoke enough that it would be silly to design your language to cater to the needs of the HTML 5 spec in particular. The fact that Rust can create DSLs via macros does help here, though I wouldn't recommend this approach for anything other than a similarly extreme case. In fact I'd say this library has the most extensive macro use of any production Rust code I've ever seen, it's quite atypical as far as Rust code goes.
vertex-four 9y ago
If Rust were solely designed for the purpose of building Servo, we'd have OO - Servo quite badly wants it for the DOM - and a whole bunch of other one-off features. In practice, Rust is a language built for systems development in general with Servo having been an early testbed to make sure it's going in the right direction.

ucarion 9y ago

It might be worth linking to the talk that discusses html5ever's use of macros? I'm having trouble finding it.

Ygg2 9y ago
Here are the slides: https://kmcallister.github.io/talks/rust/2014-rust-macros/slides.html https://kmcallister.github.io/talks/rust/2014-rust-macros/sl... Here is the video (starts around 20min): https://air.mozilla.org/bay-area-rust-meetup-november-2014/ https://air.mozilla.org/bay-area-rust-meetup-november-2014/

Ygg2 9y ago

Perhaps a better comparisson is this: https://github.com/servo/html5ever/blob/master/html5ever/src/tokenizer/mod.rs#L683 https://github.com/servo/html5ever/blob/master/html5ever/src... https://html.spec.whatwg.org/multipage/parsing.html#data-state https://html.spec.whatwg.org/multipage/parsing.html#data-sta... Where spec: U+0000 NULL -> This is an unexpected-null-character parse error. Emit the current input character as a character token. translates into: FromSet('\0') => go!(self: error; emit '\0'), If you ignore the FromSet which is used for small set of characters, and `go!` which is a macro, you get something akin to: '\0' => emit_error; emit '\0'