Rethink extends syntax

[joajfreitas]

Current syntax

protocol Foo extends Foo {
   ...
}

Considerations

• Bad error messages from parsing. There's a top level block that can start with an identifier.
• extends ?
• Do we need a name for the extension block?

Proposals

Closest

protocol::Foo extends Foo {
   ....
}

Start the block with a keyword. No name for the extension block

impl can for Foo {
}

Similar to Rust... No name for the extension block?

Start the block with a keyword. Name the extension block

impl can::Foo for Foo {
}

or

impl can Foo for Foo {
}

Although the second one is weird.

Keep the extends keyword

extend can for Foo {
}