circle

Simple: A version specifier, or feature specifiers. Backward compatibility concerns vanish when I can opt-in to a newer spec. Old code keeps working, and new code doesn't suffer for legacy nonsense. For example, the Circle compiler extends C++ with its `#feature` directive: https://github.com/seanbaxter/circle/blob/master/new-circle/... Sadly, the closest I've personally seen to this sort of thing in widespread use is `"use strict";` in JavaScript, which is only a single binary switch. You can't, say, turn on a new keyword, disable a keyword, switch to a different incompatible version of some browser API, etc. I encourage all language designers to include a feature mechanism in a forward-compatible way. Don't overthink the difficulty: It doesn't need to do anything at first, it just needs to not be a parsing error. Treat it like a comment

> But Safe C++ and Circle are different languages, right? Eh, bit of a mixed bag, I think, depending on the context in which the words are used. "Circle" can refer to the compiler/toolchain or the set of C++ extensions the compiler implements, whereas Safe C++ is either the proposal or the extensions the proposal describe. As a result, you can say that you can compile Safe C++ using Circle, and you can also describe Safe C++ as a subset of the Circle extensions. I wouldn't exactly describe the lines as well-defined, for what it's worth. > There are presumably differences between them, and I do not know what those differences are, and I do not know if those differences were documented somewhere. They're sort of documented indirectly, as far as I can tell. Compare the features in the Safe C++ proposal and the features described in the Circl

I made a facetious comment to parry that of pjmlp, whom also made a facetious comment wrt to compiler complexity and what "one person" can do. https://github.com/seanbaxter/circle It is like if one tried claiming that Fabrice Bellard was an example of a median dev. The number of C++ compilers written by one person is one. And because of this, it gives us no predictive power in what pjmlp was trying to assert. I agree with you, Albert and Lorentz and Riemann got caught in the rhetorical crossfire.