My criticism is that this language is very similar to Python and might very well confuse students who ultimately have to switch to Python or other languages.
Students switching from this to a "real world language" would be disappointed if it does not have Algebraic Data Types, pretty sure about this. Once you learned about them in SML, OCaml, Haskell or one of their descendants, which include Pyret, Elm, ReasonML/ReScript, Rust and Purescript, you feel lucky if you can use Kotlin and approximate them with sealed classes. We will see, maybe C++, Java and C# add them in the next 5 years.
C++17 added std::variant (https://en.cppreference.com/w/cpp/utility/variant) and other types so algebraic data types are now officially part of the standard. Of course, it's not as compact to write as in Pyret, especially since there's no pattern matching switch statement (yet).
they do have the godforsaken visit function which requires you to write the lambda syntax for each variant type, I end up writing chained if’s 99% of the time because it’s clearer.
There's another way using switch if I recall properly.
That said I don't like C++'s library additions just to stay modern. They are not expressive, increase build times, make debug builds slower and can fail compiler optimizers.
If it helps to think about the issue, we have a (free, online) book that manages this transition, so we've thought about this quite a bit and one co-author has been teaching a Pyret -> Python flow for several years. [https://dcic-world.org/2021-08-21/part_intro.html]
