Awesome

Why Passerine?

Passerine is a small, concise, extensible functional scripting language, powered by a VM written in Rust. Here's a small taste:

Passerine has roots in Scheme and ML-flavored languages: it's the culmination of everything I expect from a programming language, including the desire to keep everything as minimalistic and concise as possible. At its core, Passerine is lambda-calculus with pattern-matching, structural types, fiber-based concurrency, and syntactic extension.

Who started this?

Passerine was started by Isaac Clayton at the end of 2019. In August of 2022, Isaac handed over the maintenece of Passerine and its community to his friend Ben Siraphob.

A number of people have offered feedback and suggestions from time to time. Huge thanks to Raul, Hamza, Lúcás, Anton, Yasser, Shaw†, Ben, Plecra, IFcoltransG, Jack, Xal, Zack, Mahmoud and many others!

Shaw is the developer of MiniVM, a portable cross-platform runtime. The eventual goal is to retire Passerine's current virtual machine, and adopt MiniVM Assembly (VASM), then later LLVM IR, as first-class targets of the compiler.

An Overview

We've recently moved the Overview to a separate website, the Passerine Codex, which can be read online.

Note: Passerine is a work in progress: features mentioned in this overview may be unimplemented or subject to change.

FAQ

Q: Is Passerine ready for production use?

A: Not yet! Passerine is still in early stages of development, with frequent breaking changes.

Q: Is Passerine statically typed?

A: Currently Passerine is strongly and dynamically¹ typed (technically structurally typed). This is partially out of necessity – Types are defined by patterns, and patterns can be where predicated. However, I've been doing a lot of research into Hindley-Milder type systems, and the various extensions that can be applied to them.

I'm working towards making a compile-time type-checker for the language, based on Hindley-Milner type inference. With this system in place, I can make some assumptions to speed up the interpreter further and perhaps monomorphize/generate LLVM IR / WASM.

This type checker is actually the target of the next release, so stay tuned!

Q: What about algebraic effects and kind-based macros?

A: I'm interested in eventually adding both these things to the language, but first I need to implement a nice type-checker and do some more research. Algebraic Effects would fill the design space of fibers, and kind based macros would provide a more solid base for passerine's macro system. Got any fresh language features you think would complement Passerine's design philosophy? Reach out!

Q: What is vaporization memory management?

A: When I was first designing Passerine, I was big into automatic compile-time memory management. Currently, there are a few ways to do this: from Rust's borrow-checker, to µ-Mitten's Proust ASAP, to Koka's Perceus, there are a lot of new and exciting ways to approach this problem.

Vaporization is an automatic memory management system that allows for Functional but in Place style programming. For vaporization to work, three invariants must hold:

1. All functions params are passed by value via a copy-on-write reference. This means that only the lifetimes of the returned objects need to be preserved, all others will be deleted when they go out of scope.
2. A form of SSA is performed, where the last usage of any value is not a copy of that value.
3. All closure references are immutable copies of a value. These copies may be reference-counted in an acyclical manner.

With these invariants in place, vaporization ensures two things:

1. Values are only alive where they are still useful.
2. Code may be written in a functional style, but all mutations occur in-place as per rule 2.

What's most interesting is that this system requires minimal interference from the compiler when used in conjunction with a VM. All the compiler has to do is annotate the last usage of the value of any variables; the rest can be done automatically and very efficiently at runtime.

Why not use this? Mainly because of rule 3: 'closure references are immutable'. Passerine is pass-by-value, but currently allows mutation in the current scope a la let-style redefinition. But this is subject to change; and once it does, it's vaporization all the way, baby!

Q: Aren't there already enough programming languages?

A: Frankly, I think we've barely scratched the surface of programming language design. To say that Programming Language Design is saturated and at a local maxima is to not understand the nature of software development. Passerine is largely a test as to whether I can build a modern compiler pipeline. But what I'm even more interested in is the tooling that surrounds development environments.

Case in point: text-based entry for programming languages has been around forever because it's fast. However, it's not always semantically correct. The number of correct programs is an infinity smaller than the number of possible text files. Yet it's still possible to make text-based entry systems that ensure semantic correctness while encouraging exploration. In the future, we need to develop new tools that more closely blur the line between language and environment. Pharo is a step in the right direction, as are Unison and similar efforts.

I'd like to focus more on this in the future. An interesting project would be an editor/environment like Pharo/Unison for a small minimal language, like Scheme, or perhaps even Passerine.

Installation

Passerine is still very much so a work in progress. We've done a lot, but there's still a so much more to do!

For you pioneers out there, The best way to get a feel for Passerine is to install Aspen¹, Passerine's package manager and CLI. If you use a *nix-style² system, run³⁴:

cargo install aspen

This will always install the latest stable version of Passerine. To get a feel for the current state of development hell, check out a local copy for your own enjoyment:

git clone https://github.com/vrtbl/passerine

1. If you're having trouble getting started, reach out on the community Discord server.
2. Tested on Arch (btw) and macOS.
3. Now tested on Windows™!
4. In the future, we plan to distribute prebuilt binaries, but for now, a Rust install is required.

Contributing

Contributions are welcome! Read our Contribution Guide and join the Discord server to get started!