Feels like Python

How does one add immutability to a language in which the established idioms center on imperative for loops, without starting a cultural revolution? I have been mulling over this question and think I found a good answer.

It turns out that pattern matching on Python-style tuples requires existential types. This is the second time I encounter them, so I figured it is a good opportunity to show how they arise in practise.

Python’s print function is difficult to type check because it takes an arbitrary number of arbitrary arguments. We cannot give it a fixed number of type parameters, like other polymorphic functions. How can we accomodate it in a statically typed language?

I am now able to compile small but useful Newton programs that exercise the full feature set to Python! This is a major breakthrough because until now there was always something that would break when you tried something more complex.

Newton will follow Python except when there is a strong reason not to. This statement contradicts something I wrote earlier, that generators will be immutable. But now I’m beginning to think I want both behaviors. I don’t mean making mutation optional, I mean two separate languages, one with mutation and one wholly without.

When I started generating Python, I only thought of it as a stepping stone towards generating machine code or C. But over time, I realized the ability to generate Python is valuable in itself, just like Typescript does for Javascript. The question is, what degree of compatibility should I aim for?

Before I start generating C, I want to be able to loop over generator expressions. Having to iterate using C-style loops would be such an anticlimax. But there is a lot of work before I get there and I want to validate the approach first.

I mentioned previously that I am targetting C but did not give a reason. Why not use LLVM instead, or go straight to machine code?

I haven’t had much time for Newton since the last blog post, but I was able to get past something I have been working on for a while recently. I can now lower match statements to decision trees.

Without generators Newton would not feel very pythonic at all, so I consider it a must-have for the first public release.