It's definitely fun: you can also take part of the challenge to be figuring out what parts of the full language are worth adding to make the overall job easier

It's definitely fun: you can also take part of the challenge to be figuring out what parts of the full language are worth adding to make the overall job easier (so you're not taking the language subset as set in stone). When I did this for Python I started out in unrestricted Python, gradually both increasing what's implemented and reducing what's used. (Result at https://codewords.recurse.com/issues/seven/dragon-taming-with-tailbiter-a-bytecode-compiler https://codewords.recurse.com/issues/seven/dragon-taming-wit...)