Backburner Month 23: PicoML

This is an entry from a list of projects I hope to some day finish. Return to the backburnered projects index.

What is it? A tiny ML variant, designed for embedding.

It should of course have closures and anonymous functions and so forth. It should have algebraic data types—named sums, tuples, records for product types—and it should also be garbage-collected. It should have powerful pattern-matching constructs. It shouldn't be pure, in the same way that something like SML isn't pure: mutation would still need to use explicit ref types, but side-effectful functions should be allowed everywhere. It should have a basic exception system. It probably doesn't need a full module system, but some kind of namespacing would be nice.

I'm pretty neutral with respect to syntax, but I was imagining maybe borrowing some ideas from ReasonML. Over time I've become a fan of explicit delimiters for scope, but I also fully admit that syntax is probably the least interesting thing here.

Most importantly, it should be easily embeddable in any language, exposing a C API that makes it easy to initialize the runtime, call into it, and expose callbacks to it. PicoML wouldn't be for writing programs on its own: it would be for writing scripts in larger programs, which means making it accessible to larger programs should be as simple as possible.

Why write it? There are a number of language which are explicitly designed for embedding in a larger program: Lua is one of the most prominent, but there are certainly many others, my personal favorites being Wren and Io.

These embedded languages rarely have types, and the handful that do (like Pike or Mun) often don't embrace functional programming in the way that I wanted. Entertainingly, though, the closest language to what I wanted PicoML to be is Gluon, and my biggest complaint there is that it's too Haskell-ey: it's got monads and GADTs, which feels to me like it goes too far in the other direction. There's a middle ground—an impure functional language with strong SML influence—and that's where I want PicoML to sit.

Why the name? Not that surprising: I wanted to get across the idea that this would be “an extra-tiny ML variant”.

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