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june-lang

a small statically-typed (work-in-progress) language that runs on wasm

Purpose

I wanted to write a compiler that targets a VM that I didn't create myself, and I wanted to implement static type checking, neither of which I had done before. The design is roughly "Go but even simpler" and the feature set corresponds to what I think is necessary to solve Advent of Code puzzles.

Features

  • supports ahead-of-time compilation to wasm binary format
  • embeds wasmtime for jit compilation of wasm binaries
  • static typing: programs are checked during compilation
  • basic types: int, float, bool, string
  • the usual arithmetic and logical operators, loops, conditionals
  • recursion, mutual recursion, forward references for globals
  • user-defined structs
  • common collections: maps, sets, vecs
  • garbage collection
  • file i/o

Non-features

  • first-class functions
  • subtyping, interfaces
  • generics for user-defined types
  • concurrency

TODO

end-to-end for basic programs (i.e. functions, local variables, strings, basic built-ins for string processing, garbage collection):

  • scanner
  • parser
  • analyzer and type checker
  • emitter
  • emit and execute a hand-translated ast
  • wasmtime vm embedding w/external print
  • translator
  • add strings
  • generic print
  • garbage collection
  • add logging

add features:

  • return types
  • conditionals
  • loops
  • assignment
  • recursion and mutual recursion
  • forward references for globals
  • structs
  • vecs
  • maps
  • sets
  • file i/o
  • benchmarks
  • integration tests

refactoring:

  • encode call type invariants in ast
  • refactor typed ast
  • avoid copies in ast and parser
  • just one Fromio::Error in scanner
  • add back (line, col) tracking
  • better peek
  • better tokens
  • nice error reporting
  • improve the algebra
  • simplify the awful functions
  • narrow public interface
  • nicer main.rs w/structopt?
  • read and apply https://thume.ca/2019/04/18/writing-a-compiler-in-rust/
  • read and apply "rust for rustaceans" book
  • profiling and optimization

productionization:

  • skim relevant parts of engineering a compiler
  • skim relevant parts of types and programming languages

Examples

See the examples directory.

Installation

Dependencies:

  • Rust (only if building from source)

To build and install from source:

git clone [email protected]:dhconnelly/june-lang.git
cargo test
cargo install --path .

To install from crates.io:

TODO

To use a pre-built release:

TODO

Usage

june examples/hello.june

For more usage information, run junec --help. For examples, see examples/.

Previous work and references

For more details on wasm and wasmtime:

This is my eighth hobby language implementation. Here are the previous ones:

  • parents: A bytecode VM and compiler for a dynamic language. Implemented in TypeScript. Manages its own heap and implements mark-and-sweep garbage collection rather than delegating to the JS runtime. Supports first-class functions with closure and uses this to implement lists and so on. This was my first experience implementing garbage collection.
  • june-old (incomplete): A bytecode VM and compiler for a Scheme variant. Implemented in C++. Only compiles and evaluates conditionals and assignment.
  • ungulate: An interpreter for a Scheme variant, written in OCaml.
  • crab (incomplete): A bytecode VM and compiler for a simple dynamic language. Implemented in Rust. I never implemented garbage collection and assignment just copies entire values. This was my first experience writing a compiler from scratch.
  • yalig: Another interpreter for a Scheme variant, written in Go.
  • adso: A very simple interpreter implemented in JavaScript.
  • ts: Another very simple interpreter implemented in C++. This was my first experience writing an interpreter from scratch.

None of these languages are interesting: it's all Scheme variants or JavaScript lookalikes. June is my first attempt at creating a statically typed language. Despite having used a lot of languages -- I've written C, C++, Objective-C, Java, Scala, JavaScript, TypeScript, Python, and Go professionally (not counting domain-specific languages), plus Rust, Clojure, Haskell, OCaml, and Scheme for hobby stuff -- I'm less interested in language design than implementation :)

I read a lot of stuff that made this possible. Here are the resources that helped me the most:

Additionally, I've read most of SICP and poked around in the Engineering a Compiler and Modern Compiler Implementation in ML textbooks.

I also briefly worked on the GCL team at Google. (GCL is a bizarre internal language used to generate protocol buffers in a whole bunch of different scenarios, including configuration of Borg jobs as well as live experiments; there are some more details in this paper). For various reasons I didn't stay long enough to have any impact, but I was lucky to have the opportunity to review a bunch of code written by the team for a new implementation of the language, including some of the bytecode VM and compiler as well as garbage collection. This was a good (if short) learning experience.

Before that I also did an internship on the Google Web Toolkit (a Java to JavaScript compiler) team, and spent most of an internship on the Google Sheets team working on J2ObjC, a Java-to-Objective-C compiler.

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MIT

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