Starlark is a subset of Python that's only primitive recursive. And in a distributed build system, being able to guarantee termination is a very good thing. It

Starlark is a subset of Python that's only primitive recursive. And in a distributed build system, being able to guarantee termination is a very good thing. It also means Bazel can do predictable fan-outs of builds. Starlark has very good reasons for existing. CMake almost ended up using Tcl, but it was rejected because that would've introduced an external dependency, running counter to what they were trying to achieve at the time. Would Lua have been a good alternative to creating their own (rather janky) language? Sure, but Lua had very little mindshare in 2000. Even with the weird configuration language it has, it's still preferable to the horrible agglomeration of m4 macros that is Autotools. If you want to pick on any build system for not picking an existing language, Meson would be a better target, as it's similar to but not Lua, and a suitable subset of Starlark-esque subset of Lua would've been useful.