Comment by lifthrasiir

Assuming you are genuinely not aware of language implementation processes, this is called bootstrapping. You may want to implement a language A in A (a very common goal!) but this is generally impossible when you don't have a compiler for A, so you first write an implementation of A in an already implemented language B, and then use that implementation to write an A implementation in A, abandoning the initial implementation at the end. Zig just did this.