Hi Ken. Not to discourage people, but I have not seen cases where a "strong" type system would be able to scale for _real_ Smalltalk applications. You’re right. It doesn't. I'm not suggesting that. The type safety is not for app-level Smalltalk development. It's for building the VM only. I want to use the Pony concurrency model at the Smalltalk level. That’s the gist of it. Otherwise, I want a Smalltalk, not a statically compiled language. Six ref-caps that explicitly represent Pony’s concurrency model in code. They are essentially type qualifiers related specifically to concurrency. The plan is to reduce, if possible, the number of ref-caps the programmer must explicitly use/place in the code when coding a state-machine in Smalltalk, without producing a toy or straightjacket (without making it too simple or too rigid). This may require implementing the VM more as a change to (fork of) Pony instead of using Pony to implement the VM. I’m not sure yet. The six ref-cap ideas for sharing data reliably between actors are not hard to grasp, but they take some getting used to, and involve some mental load. I don't want that much (concurrency-related or any other) implementation detail in the domain layer, much in the same vein as: I don’t use Forth because I don’t want to see stack acrobatics (ROTs and DUPs, etc.) amidst domain-level state-changes (FirePhotonTorpedo). It’s distracting. It dilutes focus on the domain work/layer, and tends to cause mistakes there. The programmer’s domain logic and the concurrency-integrity provided by the ref-caps are different layers of thought and structure. The ref-caps are, however, mixed freely with domain logic in current Pony code. I think that’s a mistake. But that’s how it is now. I think of this layer mixing as an intermediate design stage of Pony. I want to abstract-out some or all ref-caps as the VM is built. Pony language is not the remarkable thing here. I see it as a better C or better Rust. It’s very good (as Algol-60-ish-looking crap-syntaxes go), but that’s not what this is about. It’s about the actor programming, the concurrency model, and the guarantees given by use of the ref-caps. We would still obviously need to respect the Pony compiler’s determination of where ref-cap use is correct or not. Your Pony program won’t compile if you don’t use the ref-caps correctly, and you don’t get the guarantees or a running program without the compile. Much easier, therefore, might be to go the other way by changing Pony to support dynamic types without violating the invariants that allow the ref-caps (under the hood, abstracted out) to make the concurrency guarantees. Work Smalltalk dynamism into Pony, instead of building a Smalltalk VM with Pony. Shaping "Rational numbers" (1/2) + (1/3) + (1/6). "--> 1 " "Complex numbers" [ :n | n * n] value: (-4 sqrt). "--> -4 " "BigNums" 111 factorial. " --> 1762952551090244663872161047107075788761409536026565516041574063347346955087248316436555574598462315773196047662837978913145847497199871623320096254145331200000000000000000000000000 " Just this is hugely complex to model in a "type safe" language. Add metaprogramming (e.g. #doesNotUnderstand:), source level debugging of live stacks and GC of large object spaces and you have a very large (space) and very slow (interlocking cache granularity) interpreter. Please prove me wrong. $0.02, -KenD