ASLAN Parser for Rust

A streaming parser for ASLAN (ASLAN Sufficiently Lax AI Notation) - an LLM stream compatible structured data format.

See the full specification in the main repository.

Installation

Add this to your Cargo.toml:

[dependencies]
aslan = "0.1.0"

Usage

Basic Parsing

use aslan::ASLANParser;

let mut parser = ASLANParser::new();
let result = parser.parse("[asland_greeting]Hello [asland_name]World!");

// Result is a serde_json::Value:
// {
//   "_default": null,
//   "greeting": "Hello ",
//   "name": "World!"
// }

Streaming with parse_next

ASLAN is designed for streaming LLM outputs. Use parse_next to feed tokens incrementally:

use aslan::ASLANParser;

let mut parser = ASLANParser::new();

// Simulate streaming tokens from an LLM
parser.parse_next("[asland_");
parser.parse_next("response]");
parser.parse_next("Here is ");
parser.parse_next("the answer.");

parser.close();
let result = parser.get_result();

Event Listeners

Subscribe to events for real-time processing:

use aslan::ASLANParser;

let mut parser = ASLANParser::new();

// Listen for content updates
parser.add_content_listener(|event| {
    println!("Field: {}, Content: {}", event.field_name, event.content);
});

// Listen for field completions
parser.add_end_listener(|event| {
    println!("Completed: {} = {}", event.field_name, event.content);
});

parser.parse("[asland_msg]Hello!");

Nested Objects and Arrays

use aslan::ASLANParser;

let mut parser = ASLANParser::new();

// Objects
let result = parser.parse(
    "[asland_user][aslano][asland_name]Alice[asland_age]30"
);
// { "user": { "name": "Alice", "age": "30" } }

// Arrays
let mut parser = ASLANParser::new();
let result = parser.parse(
    "[asland_items][aslana][asland]Apple[asland]Banana[asland]Cherry"
);
// { "items": ["Apple", "Banana", "Cherry"] }

Parser Settings

use aslan::{ASLANParser, ASLANParserSettings};

let mut parser = ASLANParser::with_settings(ASLANParserSettings {
    strict_start: true,           // Require [aslang] to start parsing
    strict_end: true,             // Stop parsing at [aslans]
    collapse_whitespace: true,    // Collapse whitespace at object/array starts
    ..Default::default()
});

Features

• Streaming-first: Parse character-by-character, perfect for LLM token streams
• Fault-tolerant: Designed to handle malformed input gracefully
• Event-driven: Subscribe to content, end, and end_data events
• Nested structures: Full support for objects, arrays, and mixed nesting
• Instructions: Emit metadata events without affecting the data structure
• Comments & Escapes: Skip content or escape ASLAN delimiters

ASLAN Delimiters

License

MIT