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# Dust
High-level programming language with effortless concurrency, automatic memory management and type
safety.
Dust is a high-level interpreted programming language with static types that focuses on ease of use,
performance and correctness.
Dust is a work in progress. Because it aims to deliver a high level of safety, extensive testing
is required. The language is still in the design phase, and the syntax is subject to change.
## Implementation
## Usage
Dust is implemented in Rust and is divided into several parts, primarily the lexer, compiler, and
virtual machine. All of Dust's components are designed with performance in mind and the codebase
uses as few dependencies as possible.
The Dust command line tool can be used to run Dust programs. It is not yet available outside of
this repository.
### Lexer
```sh
cargo run --package dust-shell -- examples/hello_world.ds
```
The lexer emits tokens from the source code. Dust makes extensive use of Rust's zero-copy
capabilities to avoid unnecessary allocations when creating tokens. A token, depending on its type,
may contain a reference to some data from the source code. The data is only copied in the case of an
error, because it improves the usability of the codebase for errors to own their data when possible.
In a successfully executed program, no part of the source code is copied unless it is a string
literal or identifier.
```sh
cargo run --package dust-shell -- -c '"Hello my name is " + read_line() + "!"'
```
### Compiler
Dust is easily embedded in another program. You can run a dust program of any size or complexity
with a single function.
The compiler creates a chunk, which contains all of the data needed by the virtual machine to run a
Dust program. It does so by emitting bytecode instructions, constants and locals while parsing the
tokens, which are generated one at a time by the lexer.
```rust
use dust_lang::{run, Value};
#### Parsing
fn main() {
let code = "
let x = 'Dust'
let y = ' is awesome!'
Dust's compiler uses a custom Pratt parser, a kind of recursive descent parser, to translate a
sequence of tokens into a chunk.
write_line(x + y)
#### Optimizing
42
";
When generating instructions for a register-based virtual machine, there are opportunities to
optimize the generated code, usually by consolidating register use or reusing registers within an
expression. While it is best to output optimal code in the first place, it is not always possible.
Dust's compiler has a simple peephole optimizer that can be used to modify isolated sections of the
instruction list through a mutable reference.
let result = run(code);
### Instructions
assert_eq!(result, Ok(Some(Value::integer(42))));
}
```
### Virtual Machine
## Concepts
## Previous Implementations
### Effortless Concurrency
## Inspiration
Dust makes concurrency as effortless as possible. Dust is organized into **statements**, and any
sequence of statements can be run concurrently by simply adding the `async` keyword before the block
of statements.
```rust
// Counts from 0 to 9, sleeping for an increasing amount of time between each.
let count_slowly = fn (multiplier: int) {
i = 0
while i < 10 {
sleep(i * multiplier)
write_line(i.to_string())
i += 1
}
}
async {
count_slowly(200) // Finishes last
count_slowly(100) // Finishes second
count_slowly(50) // Finishes first
}
```
### Automatic Memory Management
Dust uses a garbage collector to automatically manage memory.
```rust
let x = 0 // x is assigned but never used
// x is removed from memory
let y = 41 // y is assigned
let z = y + 1 // y is kept alive for this statement
// y is removed from memory
write_line(z) // z is kept alive for this statement
// z is removed from memory
```
### Type Safety
Dust is statically typed and null-free, but the type of a value can usually be inferred from its
usage. Dust will refuse to run programs with type errors, but will usually not require type
annotations.
```rust
// These two statements are identical to Dust
let x = 1
let x: int = 1
// Numbers with decimals are floats
let y = 10.0
let y: float = 10.0
// Strings are enclosed in double quotes and are guaranteed to be valid UTF-8
let z = "Hello, world!"
let z: str = "Hello, world!"
```
Aside from the ubiqutous `bool`, `int`, `float`, and `str` types, Dust also has lists, maps,
ranges, structures, enums and functions.
- [The Implementation of Lua 5.0](https://www.lua.org/doc/jucs05.pdf)
- [A No-Frills Introduction to Lua 5.1 VM Instructions](https://www.mcours.net/cours/pdf/hasclic3/hasssclic818.pdf)
- [Crafting Interpreters](https://craftinginterpreters.com/)