"What RPython allows one to do is profoundly different to the traditional route. In essence, one writes an interpreter and gets a JIT for free. I suggest reread

"What RPython allows one to do is profoundly different to the traditional route. In essence, one writes an interpreter and gets a JIT for free. I suggest rereading that sentence again: it fundamentally changes the economics of language implementation for many of us. To give a rough analogy, it is like moving from manual memory management to automatic garbage collection." (RPython being the foundation of PyPy.)