> Why can't I just run Ruby 3.0 with a flag that tells it to emulate Ruby 2.6? Or 1.8 for that matter? I suspect it would be a nightmare - it's not just small

> Why can't I just run Ruby 3.0 with a flag that tells it to emulate Ruby 2.6? Or 1.8 for that matter? I suspect it would be a nightmare - it's not just small parts of the code, it would be other parts of the code that depend on it. Take for instance Python 2 & Python 3's approach to if ("hello" > "goodbye") - in Python 2 that would be False and in Python 3 that would be TypeError. So if you are running Python 3 with a Python 2.7 flag, how should Python's internal modules that are written in Python 3 handle this? Do all Python's internal modules need to work on every legacy version of Python and load the correct version, or does the interpreter need to somehow load up instructions for both and parse them together? Then there is the whole problem about libraries - are these allowed to selectively choose which version of python they run on? This is of course only one small example of the complexity - If it was easy to make these things backwards compatible it would be great, but I would expect the cost for implementing full backwards compatibility to be high and the language authors are probably motivated to make people move towards the latest versions.