at

at (from @) is a programming language designed for AI agents — explicit, readable, and greppable.

• Agent-first: Code should be readable and writable without IDE support
• Explicit effects: needs/using make dependencies visible and mockable
• Greppable: Clear imports, no barrel files, no implicit magic
• Predictable: Results over exceptions, minimal magic
• Fast: Cold start in milliseconds, small binary footprint

npm install -g @aryaminus/at

Use at binaries for CLI usage; the npm package provides WASM bindings.

brew tap aryaminus/at
brew install at

at --version
at --help

# Run a program
at run examples/sum.at

# Type-check (fails on errors; warns are non-fatal)
at check file.at

# Run tests (file or directory)
at test file.at
at test tests/

# Start REPL
at repl

# Format code
at fmt file.at

# Run benchmarks
at bench file.at --runs 10

# Show dependencies
at deps file.at

# Lint code
at lint file.at

# Manage cache
at cache list
at cache prune --max-files 100

# Start MCP server
at mcp-server tools.at

# Start LSP server
at lsp

# Get help
at --help
at run --help

fn greet(name: string) -> string {
    return "Hello, " + name + "!";
}

fn safe_div(a: int, b: int) -> result<int, string> {
    return if b == 0 {
        err("division by zero")
    } else {
        ok(a / b)
    };
}

fn process(items: array<int>) -> int {
    let sum = 0;
    for item in items {
        set sum = sum + item;
    }
    return sum;
}

test "greeting works" {
    let msg = greet("World");
    assert_eq(msg, "Hello, World!");
}

test "division handles errors" {
    let result = safe_div(10, 0);
    assert(is_err(result));
}

fn main() {
    print(greet("at"));
    
    let numbers = [1, 2, 3, 4, 5];
    let total = process(numbers);
    print(total);
    
    return 0;
}

Canonical install docs live in docs/install.md.

cargo install --git https://github.com/aryaminus/at --bin at

Download from GitHub releases for your platform:

# macOS (Intel)
curl -L https://github.com/aryaminus/at/releases/latest/download/at-x86_64-apple-darwin.tar.gz | tar xz
sudo mv at-x86_64-apple-darwin /usr/local/bin/at

# macOS (Apple Silicon)
curl -L https://github.com/aryaminus/at/releases/latest/download/at-aarch64-apple-darwin.tar.gz | tar xz
sudo mv at-aarch64-apple-darwin /usr/local/bin/at

# Linux
curl -L https://github.com/aryaminus/at/releases/latest/download/at-x86_64-unknown-linux-gnu.tar.gz | tar xz
sudo mv at-x86_64-unknown-linux-gnu /usr/local/bin/at

Releases are automated on merges to main. A version bump commit and vX.Y.Z tag are created by CI.

All core features implemented:

• Types: int, float, bool, string, unit, array<T>, option<T>, result<T,E>
• Control flow: if (expression, optional else), while, for, break, continue
• Pattern matching: match with ok, err, some, none, _ patterns; multi-field enum variants
• Error handling: ? (try) operator, option, result
• Staged deprecation warnings for legacy throw and try { ... } catch { ... } usage
• Effects: needs/using for capability management
• Imports: Local paths and URLs with caching
• Comments: // line and /* */ block comments
• String escapes: \n, \t, \r, \0, \\, \"
• Arrays: Immutable arrays with len, append, contains, slice
• Mixed arithmetic: int and float can be mixed freely (int promoted to float)
• Operators: +, -, *, /, %, &&, ||, ==, !=, <, <=, >, >=
• Test blocks: test "name" { ... } with assert and assert_eq; multi-file test discovery (at test <dir>)
• Tool functions: tool fn for MCP integration
• Regular expressions: regex_match, regex_find, regex_replace with capture group support
• 40+ builtins: math (abs, min, max, floor, ceil, round, pow, sqrt, sum), string (join, replace, starts_with, ends_with, repeat, parse_float), character (char_code, from_char_code, is_digit, is_alpha, is_upper, is_lower), array (sort, reverse, index_of, count, range), and more

Staged deprecation status (compatibility mode):

• legacy_exception_surface and unqualified_import_call are warning-level in 0.1.x.
• Planned enforcement timeline:
  • 0.2.x: optional deny mode for migration testing.
  • 0.3.0 or later: may become hard errors by default.

Comprehensive tooling for development, testing, and deployment:

• Formatter: Consistent, stable formatting (at fmt)
• LSP: Diagnostics, hover, goto-definition, completion, inlay hints (at lsp)
• Type checker: Full type inference and checking (at check)
• Linter: Detect duplicate names, unused variables (at lint)
• MCP server: Expose tools to AI agents (at mcp-server)
• VM: Stack-based interpreter (at run)
• REPL: Interactive development (at repl)
• Test runner: Run test blocks (at test)
• Benchmark: Performance measurement (at bench)
• Deps: Show module dependencies (at deps)
• Cache: Manage cached remote imports (at cache)
• WASM: Browser-compatible runtime

CI enforces:

• cargo fmt --check
• cargo clippy correctness gate
• non-correctness clippy warning budget (.clippy-warning-baseline.toml)
• workspace tests + example run/check sweep
• release binary size budget (<= 8,500,000 bytes)
• benchmark stability threshold via examples/run_bench.sh + examples/bench_compare.py

• docs/lang.md — Complete language reference
• docs/cli.md — CLI commands and options
• docs/install.md — Installation and platform notes
• examples/features.at — Comprehensive feature demonstration

From "A Language For Agents":

1. Context Without LSP: Readable without IDE support
2. Braces, Not Whitespace: No indentation sensitivity
3. Explicit Flow Context: needs/using for effects
4. Results Over Exceptions: Typed error handling
5. Minimal Diffs: Trailing commas encouraged
6. Greppable: No barrel files, explicit imports
7. Local Reasoning: No macros, no implicit magic

MIT