Rewind to 2006. Should we implement Python in Python? Of course not; it's not useful! PyPy should not be done! It's literally 50 times slower than CPython!

Fortunately, the PyPy folks have stuck with it, and PyPy is now faster than CPython across the board. Many other languages have also been implemented using its considerable infrastructure. Compiler experts have been minted from scratch. Should it have been done? Yes.

Even with the vulgar assumption that "practical utility" is the only source of good, this type of project is good.

"Metascala is barely 3000 lines of Scala, and is complete enough that it is able to interpret itself metacircularly. [...]

The goal of Metascala is to create a platform to experiment with the JVM: a 3000 line JVM written in Scala is probably much more approachable than the 1,000,000 lines of C/C++ which make up HotSpot, the standard implementation, and more amenable to implementing fun features like continuations, isolates or value classes."

That seems pretty neat to me.

Any reason why it SHOULDN'T be done? I fail to see any downsides to its existence.

"Why not?" is a perfectly good response to "why?", especially on a site called hacker news.

The point, from the project page:

> The goal of Metascala is to create a platform to experiment with the JVM: a 3000 line JVM written in Scala is probably much more approachable than the 1,000,000 lines of C/C++ which make up HotSpot, the standard implementation, and more amenable to implementing fun features like continuations, isolates or value classes.

My take on this: Experimentation is a form of learning. Whilst the end product may seem trivial, there may be meaningful discoveries during the journey.