> I wonder then, if all that talent is not better served by implementing a BETTER version of the core 50% or 70% Ruby language as a new language, getting rid of edge cases and garbage.

I would very much like to see that. But I think we first need more competition to MRI.

E.g. note the proposal for "refinements" for Ruby 2.1 which is an implementation nightmare for anyone that wants a fast implementation. See Charles Nutter's (of jRuby fame) comments about it, for example. Since MRI is as slow as it is, there's little incentive to keep features like that out - it won't kill MRI performance.

It's also hard to determine exactly what the viable subset should be, since most those of us who would like a faster Ruby also love Ruby a lot because of how dynamic it is, when it is used right, and jump ship if the language lost too much flexibility in the quest for that performance.

Part of my own motivation for writing about writing a Ruby compiler is exploring what parts of Ruby can be implemented efficiently because frankly it's hard to even guess exactly how an "efficient Ruby" should look.

There are some obvious problems for implementations that want to boost performance, like too much reliance on eval() and defining eigenclasses on objects, as well as autoload, require and include, all of which can worst case trash all method caching and optimisations all over the place.

But throwing out all of that would be brutal, especially given common Ruby patterns likes dynamically require'ing everything in a directory at application startup, which should be fine, vs. a "require" occurring later in execution. And it's not clear that there aren't other common patterns that'll cause a lot of pain.

I think we will see at least implementations with options to disable support for certain things, or with support to let applications declare "from now on, no shenanigans" to let the implementation take shortcuts, would be very helpful.

There's a lot of things developers could do themselves, that would let even a compliant implementation speed up. E.g. call #freeze on all classes you have no intention of modifying somewhere that is easily identified by relatively superficial analysis would make a massive difference (suddenly you can cache lots of extra methods, and even inline and unroll things like "each" loops in many cases that'd otherwise be an expensive flurry of method calls).

Other things are about developer practice: Freeze all objects you don't want to modify ASAP on creation. A good implementation could make good use of that too.
But today there is no incentive for Ruby users to write Ruby that is amenable to fast execution because the implementations don't take advantage of it.

Once there is an implementation that makes the advantages of writing Ruby to a subset that is more amenable to fast execution, then I think it'd be possible to get traction for deprecating and removing features that are a performance nightmare.

> Matter of fact, didn't Matz do something like that, with an embedded-oriented Ruby like language recently?

Sort of, though mruby appears to focus on size and ability to embed rather than specifically picking a subset that's amenable to a fast implementation. It's still a bytecode interpreter, for example, and it's not even aiming for complying with the (already limited) ISO standard for Ruby.