Comment by Maxatar

Yes, the compiler contains an interpreter for the entire language, not just a subset. It is circular as you rightly point out, but there's no contradiction here.

Typically the interpreter limits itself to only evaluating pure functions or functions that do not perform any kind of IO, but in principle this restriction is not necessary. For example Jai's compiler allows completely arbitrary execution at compile time including even downloading arbitrary data from the Internet and using that data to make decisions about how to compile code.