Auto Language Specification

Version: 0.2 Status: Draft Last Updated: 2026-04

Table of Contents

1. Introduction
2. Language Overview
3. Lexical Structure
4. Grammar (EBNF)
5. Types
6. Expressions
7. Statements
8. Control Flow
9. Functions
10. Data Structures
11. Type Definitions
12. Enums
13. Specs (Traits)
14. Generics
15. Closures
16. Option and Result
17. Concurrency: Tasks and Async
18. Compile-Time Metaprogramming
19. Ownership and Borrowing
20. Modules and Imports
21. UI Widgets and Routing
22. Nodes (Atom Format)
23. Memory Management
24. Implementation Comparison

---

Introduction

Auto is a multi-paradigm programming language designed for automation and flexibility. It provides a unique blend of static and dynamic typing with multiple language variants:

• AutoLang: Static/dynamic hybrid that transpiles to C and Rust
• AutoScript: Dynamic scripting language for embedding
• AutoConfig: JSON superset for configuration
• AutoShell: Cross-platform shell scripting
• AutoDSL: Domain-specific language for UI applications

Design Philosophy

Auto is designed around four core principles:

1. Flexibility: Support multiple programming paradigms and use cases
2. Safety: Memory safety with both manual and automatic management options
3. Performance: Zero-cost abstractions and efficient compilation
4. Interoperability: Seamless integration with C and Rust ecosystems

Implementations

Auto has three implementations:

1. Rust Implementation (crates/auto-lang/): Reference implementation, hand-written
2. C Implementation (autoc/): AI-generated, portable, incomplete but functional
3. Self-Hosted (auto/): Compiler written in Auto itself (early stage)

---

Language Overview

Hello World

// Traditional approach
fn main() {
    print("Hello, World!")
}

// Expression-based (script mode)
print("Hello, World!")

Key Features

• Six Storage Modifiers: let, var, const, mut, shared, static for different mutability and lifetime semantics
• Type Inference: Automatic type deduction with optional explicit annotations
• Pattern Matching: Powerful is expression for pattern matching with struct destructuring
• F-Strings: First-class string interpolation with embedded expressions
• Ranges: First-class range expressions 0..10 and 0..=10
• Option/Result: ?T for optional values, !T for error-propagating results (Plan 120)
• Generics: Parameterized types and functions with type and const parameters
• Specs (Traits): Interface-like type constraints with polymorphic dispatch
• Ownership Trinity: view/mut/move resource access semantics (Plan 122)
• Concurrency: Task/Actor model with spawn/send, async/await (Plans 121/124/126)
• Compile-Time: #if/#for/#is/#{} for metaprogramming (Plan 095)
• C/Rust Interop: Seamless integration with C and Rust code

---

Lexical Structure

Source Code Representation

Auto source files use the .at extension and are encoded as UTF-8.

Whitespace

• Spaces: Regular space character (U+0020)
• Tabs: Tab character (U+0009)
• Newlines: Line feed (U+000A) or carriage return + line feed (U+000D U+000A)

Newlines are significant in Auto - they act as statement terminators (like semicolons in other languages).

Comments

// Single-line comment

/// Doc comment

/*
   Multi-line comment
   Spans multiple lines
*/

Identifiers

Identifiers start with a letter or underscore, followed by letters, digits, underscores, or hyphens.

identifier → (letter | "_") (letter | digit | "_" | "-")*

Hyphens are allowed within identifiers (no surrounding spaces): preview-card is a single identifier. With spaces, a - b is subtraction.

Examples: foo, _bar, data123, my_variable, preview-card

Keywords

Auto reserves 55 keywords (from token.rs), organized by category:

Declarations: fn, let, mut, const, var, type, union, enum, tag, alias, spec, ext, static, shared, impl, nodeControl Flow: if, else, for, break, is, in, on, as, toOwnership: view, mut, move, copy, take, holdLiterals: true, false, nil, nullOption/Result: None, Some, Ok, ErrConcurrency: task, spawn, await, reply, goModules: use, pac, super, dep, hasBoolean Logic: and, orUI/Routing: routes, outlet, link, route, navOther: grid

Operators and Punctuation

Arithmetic Operators

Operator	Description
+	Addition
-	Subtraction/negation
*	Multiplication
/	Division
%	Modulo

Comparison Operators

Operator	Description
==	Equal comparison
!=	Not equal
<	Less than
>	Greater than
<=	Less than or equal
>=	Greater than or equal

Assignment Operators

Operator	Description
=	Assignment
+=	Addition assignment
-=	Subtraction assignment
*=	Multiplication assignment
/=	Division assignment
%=	Modulo assignment

Logical Operators

Operator	Description
!	Logical NOT
&&	Logical AND (also: and keyword)
`

Range Operators

Operator	Description
..	Range (exclusive)
..=	Range (inclusive)

Null-Safe / Error Propagation Operators (Plan 120)

Operator	Description
?	Question mark (Option/Result suffix)
??	Null coalescing
?.	Safe navigation / null-safe access
.?	Error propagation

Ownership Dot-Operators (Plan 122)

Operator	Description
.view	Immutable borrow (&T)
.mut	Mutable borrow (&mut T)
.move	Ownership transfer
.take	DEPRECATED — use .move

Arrow Operators

Operator	Description
->	Arrow: function return type annotation (fn foo() -> int), event routing (src -> dest)
=>	Double arrow: closures (x => expr)
->	Arrow: pattern match branches (42 -> body), event routing (src -> dest)

Punctuation

Symbol	Description
.	Member access
:	Colon (field-value pairs, type annotations)
`	`
@	At sign (annotations)
#	Hash sign (annotations, compile-time)
~	Tilde (async/future type marker)
,	Comma
;	Semicolon
( )	Parentheses
[ ]	Square brackets
{ }	Curly braces

Compile-Time Tokens (Plan 095)

Token	Description
#if	Compile-time conditional
#for	Compile-time loop
#is	Compile-time pattern match
#{	Compile-time expression block

Literals

Integer Literals

integer → digit+ ("u" | "u8" | "i8")?
       | "0x" hex_digit+          // hexadecimal
       | digit ("_" digit)* digit? // underscore separators

42          // i32 (default)
42u         // u32
42u8        // u8
42i8        // i8
0x1A        // hexadecimal (26)
1_000_000   // underscore separators

Floating-Point Literals

float → digit+ "." digit* ("f" | "d")? (exponent)?
     | digit+ ("f" | "d")              // suffix on integer
exponent → ("e" | "E") ("+" | "-")? digit+

3.14        // float (default)
3.14f       // float (explicit suffix)
3.14d       // double
3.14e-10    // scientific notation
1.0e5       // scientific notation
42f         // float from integer
42d         // double from integer

String Literals

string       → '"' .* '"'
multi_string → '"""' .* '"""'
cstr         → 'c' '"' .* '"'

"Hello, World!"           // Regular string (with length)
"""Hello
World"""                  // Multi-line string (Plan 169)
c"Hello, World!"          // C string (null-terminated, no escape processing)

Multi-line strings (triple-quoted, Plan 169):

• Preserve literal newlines
• Allow embedded 1-2 consecutive double quotes
• Process standard escape sequences (\n, \t, etc.)

Character Literals

char → "'" (letter | digit | escape_sequence) "'"

'a'         // Simple character
'\n'        // Escape sequence
'Z'
'0'

Boolean Literals

true
false

Nil/Null Literals

nil    // Auto's zero-size type
null   // Nullable pointer value

---

Grammar (EBNF)

Notation

The following EBNF notation is used:

• * - zero or more
• + - one or more
• ? - optional (zero or one)
• | - alternation
• () - grouping
• [] - character class

Complete Grammar

Program        → (Stmt)*

Stmt           → VarStmt
               | IfStmt
               | ForStmt
               | WhileStmt
               | BlockStmt
               | ExprStmt
               | UseStmt
               | FnStmt

VarStmt        → ("let" | "mut" | "const" | "var") IDENTIFIER Type? "=" Expr

IfStmt         → "if" Expr Stmt ("else" Stmt)?

ForStmt        → "for" IDENTIFIER? "in" Expr Stmt

WhileStmt      → "while" Expr Stmt

BlockStmt      → "{" (Stmt)* "}"

ExprStmt       → Expr

UseStmt        → "use" STRING

FnStmt         → "fn" IDENTIFIER "(" ParamList? ")" Type? BlockStmt

ParamList      → Param ("," Param)*

Param          → IDENTIFIER Type

Expr           → Assignment

Assignment     → LogicalOr (("=" | "+=" | "-=" | "*=" | "/=") LogicalOr)?

LogicalOr      → LogicalAnd ("||" LogicalAnd)*

LogicalAnd     → Equality ("&&" Equality)*

Equality       → Comparison (("==" | "!=") Comparison)*

Comparison     → Range (("<" | ">" | "<=" | ">=") Range)?

Range          → Additive (".." | "..=") Additive?

Additive       → Multiplicative (("+" | "-") Multiplicative)*

Multiplicative → Unary (("*" | "/") Unary)*

Unary          → ("!" | "-" | "+") Unary
               | Call

Call           → Primary ("(" ArgList? ")" | "[" Expr "]" | "." IDENTIFIER)*

ArgList        → Expr ("," Expr)*

Primary        → INTEGER
               | FLOAT
               | STRING
               | CHAR
               | "true"
               | "false"
               | "nil"
               | "null"
               | IDENTIFIER
               | ArrayExpr
               | ObjectExpr
               | FStrExpr
               | RangeExpr
               | "(" Expr ")"
               | "is" PatternMatch

ArrayExpr      → "[" (Expr ("," Expr)*)? "]"

ObjectExpr     → "{" (IdentValuePair ("," IdentValuePair)*)? "}"

IdentValuePair → IDENTIFIER ":" Expr

FStrExpr       → "f" '"' FStrPart* '"'

FStrPart       → STRING
               | "{" Expr "}"

RangeExpr      → Expr (".." | "..=") Expr?

PatternMatch   → Expr "{" (PatternBranch ("," PatternBranch)*)? "}"

PatternBranch  → Pattern "->" Expr

Pattern        → Literal
               | IDENTIFIER
               | "as" Type
               | "in" Range
               | Condition

---

Types

Type System Overview

Auto has a hybrid type system:

• Static mode: Type checking at compile time (default for AutoLang)
• Dynamic mode: Type checking at runtime (script mode with var)

The type system includes 37 type variants from ast/types.rs, covering primitives, compound types, generics, and special types.

Primitive Types

Auto Type	C Type	Rust Type	Description
int	int32_t	i32	Signed 32-bit integer
uint	uint32_t	u32	Unsigned 32-bit integer
byte	uint8_t	u8	8-bit unsigned integer
i8	int8_t	i8	8-bit signed integer
i16	int16_t	i16	16-bit signed integer
i64	int64_t	i64	64-bit signed integer
u16	uint16_t	u16	16-bit unsigned integer
u64	uint64_t	u64	64-bit unsigned integer
usize	size_t	usize	Pointer-sized unsigned integer
float	double	f64	64-bit floating-point
double	double	f64	Alias for float
bool	bool	bool	Boolean (true/false)
char	char	char	Single character
void	void	()	Unit/void type
nil	(no equivalent)	!	Zero-size type

String Types

Auto Type	C Type	Rust Type	Description
str	struct { len; data; }	&str	String slice with length
String	char* (dynamic)	String	Owned dynamic string (Plan 155)
cstr	const char*	&CStr	C string (null-terminated)

Compound Types

Array Types

[N]T        // Static array: fixed size N, type T (e.g., [10]int)
[expr]T     // Runtime-sized array: size determined at runtime (Plan 052)
[]T         // Slice: borrowed view into an array

let fixed [5]int = [1, 2, 3, 4, 5]
let slice []int = fixed[1..3]    // borrowed slice

List Type (Dynamic)

List<T>     // Growable list (heap-backed)

let list = List.new()
list.push(1)
list.push(2)
let len = list.len()    // 2

Map Type (Plan 160)

Map<K, V>   // Typed key-value dictionary

let scores Map<str, int> = Map.new()
scores.set("Alice", 95)

Pointer and Reference Types

*T          // Raw pointer
&T          // Reference (immutable borrow)

let val = 42
let ptr *int = &val
let ref &int = val.view

Option Type (Plan 120)

?T          // Optional value: Some(T) or None

let name ?str = Some("Alice")
let empty ?str = None

Result Type (Plan 120)

!T          // Error-propagating: Ok(T) or Err(...)

fn divide(a int, b int) !int {
    if b == 0 {
        return Err("division by zero")
    }
    Ok(a / b)
}

Handle Type (Plan 121)

Handle<T>   // Reference to a running task

let handle Handle<CounterTask> = spawn CounterTask()
handle.send(Increment(1))

Linear Type

linear<T>   // Move-only semantics (no implicit copy)

Function Types

fn(params) ret   // Function type signature

let callback fn(int, int) int = add

Generic Type Instances

MyType<T>           // Generic type with type parameter
MyType<T, N u32>    // Generic type with type + const parameter

Type Annotations

// Type inference
let x = 42

// Explicit type annotation (space-separated)
let y int = 42

// Function with type annotations (space-separated)
fn add(a int, b int) int {
    a + b
}

Type Coercion

Auto performs automatic type coercion for assignments:

let b byte = 42    // OK: int coerced to byte
let i int = b      // OK: byte promoted to int

---

Expressions

Auto supports 55 expression types (from ast.rs Expr enum). This section documents all major expression categories.

Literal Expressions

42          // int (i32)
42u         // uint (u32)
42u8        // byte (u8)
42i8        // i8
3.14        // float
3.14d       // double
'x'         // character
"hello"     // string
c"hello"    // C string (null-terminated)
true        // boolean
false       // boolean
nil         // nil value

Identifier Expressions

x
my_variable
_underscore
preview-card    // hyphens allowed within identifiers

Arithmetic Expressions

let sum = 10 + 5
let diff = 10 - 5
let product = 10 * 5
let quotient = 10 / 5
let remainder = 10 % 5

Comparison Expressions

10 == 5    // false
10 != 5    // true
10 < 5     // false
10 > 5     // true
10 <= 10   // true
10 >= 10   // true

Logical Expressions

true && false    // false
true || false    // true
!true            // false
true and false   // keyword form
true or false    // keyword form

Assignment Expressions

x = 10
x += 5    // x = x + 5
x -= 5    // x = x - 5
x *= 5    // x = x * 5
x /= 5    // x = x / 5
x %= 5    // x = x % 5

Range Expressions

// Exclusive range: 0, 1, 2, 3, 4
let r1 = 0..5

// Inclusive range: 0, 1, 2, 3, 4, 5
let r2 = 0..=5

// Using ranges in for loops
for i in 0..10 {
    print(i)
}

F-String Expressions

let name = "World"
let msg = f"Hello, $name!"         // "Hello, World!"

let a = 5
let b = 10
let result = f"${a} + ${b} = ${a + b}"  // "5 + 10 = 15"

// Backtick syntax
let msg2 = `Hello, ${name}!`

Array Expressions

let arr = [1, 2, 3, 4, 5]
let empty = []
let strings = ["hello", "world"]
let first = arr[0]           // 1
let slice = arr[1..3]        // [2, 3]

Object Expressions

let obj = {
    name: "John",
    age: 30,
    active: true
}
let name = obj.name          // "John"

Grouping Expressions

let result = (2 + 3) * 5    // 25

Unary Expressions

let neg = -x        // negation
let not = !flag     // logical NOT

Dot Expressions (Member Access / Method Call)

obj.field           // field access
obj.method()        // method call
list.push(1)        // method with argument

Ownership Expressions (Plan 122)

let ref_val = x.view     // immutable borrow (&T)
let mut_ref = x.mut      // mutable borrow (&mut T)
let owned = x.move       // ownership transfer

Type Conversion Expressions

let n = x.as(int)        // zero-cost reinterpret (.as)
let s = 42.to(str)       // explicit conversion (.to)

Option/Result Expressions (Plan 120)

// Constructors
let val = Some(42)       // wrap in Option
let empty = None         // empty Option
let ok = Ok(42)          // success Result
let err = Err("failed")  // error Result

// Null coalescing
let x = maybe_val ?? 0   // default if None

// Error propagation
let result = expr.?      // propagate Err as return

// Safe navigation
let name = obj?.name     // access if not None

Closure Expressions

// Simple closure
let add = (a, b) => a + b

// Typed closure
let multiply = (a int, b int) => int { a * b }

// Single-param closure (no parens needed)
let double = x => x * 2

If Expressions

let result = if x > 0 { 1 } else { 0 }

// Multi-branch
let label = if x > 0 {
    "positive"
} else if x < 0 {
    "negative"
} else {
    "zero"
}

Block Expressions

let result = {
    let x = 10
    let y = 20
    x + y       // last expression is the value
}

Null Coalescing Expressions (Plan 120)

let value = maybe ?? default    // use default if None

Error Propagation Expressions (Plan 120)

let result = expr.?    // if Err, return early; if Ok, unwrap

Smart Pointer Expressions

let boxed = Box(value)    // heap allocation
let shared = Arc(value)   // reference-counted

Async Expressions (Plan 124)

// Async block
let future = ~{
    let data = fetch().await
    process(data)
}

// Await a future
let result = future.await

// Spawn to background (Plan 126)
let handle = task.go

Compile-Time Expressions (Plan 095)

let value = #{ 1 + 2 }    // evaluated at compile time

Node Expressions

// Node construction
widget(attr: "value") {
    child()
}

Grid Expressions

let grid = grid(a: "first", b: "second") {
    [1, 2, 3]
    [4, 5, 6]
}

Hold Expressions

let val = expr.hold    // extend lifetime binding

Precedence Table

Precedence	Operators	Associativity
1 (highest)	.view, .mut, .move, .await, .go, .hold	Left
2	! (NOT), - (negate)	Right
3	*, /, %	Left
4	+, -	Left
5	<, >, <=, >=	Left
6	==, !=	Left
7	&&, and	Left
8	`
9	??	Left
10	.., ..=	Left
11 (lowest)	=, +=, -=, *=, /=, %=	Right

---

Statements

Auto supports 34 statement types (from ast.rs Stmt enum).

Variable Declarations

Auto provides six storage modifiers with different semantics:

let - Immutable Binding

let x = 42
let name str = "Alice"
// Error: x = 10  // cannot reassign

var - Mutable Binding

var x = 42
x = 10    // OK

const - Compile-Time Constant

const MAX_SIZE = 100
const GREETING str = "Hello"
// Error: MAX_SIZE = 200  // cannot modify

mut - Mutable Reference Keyword

mut x = 42
x = 10    // OK

Note: var and mut are both mutable. var is preferred for script mode; mut for typed mode.

shared - Static/Shared Storage (Plan 168)

shared counter int = 0
shared cache Map<str, str> = Map.new()

shared creates process-lifetime static storage. Transpiles to Rust static with Lazy<Mutex&lt;T&gt;>.

static - Static Member (in type context)

Used inside type definitions for static methods:

type Point {
    x int
    y int

    static fn new(x int, y int) Point {
        Point(x, y)
    }
}

Expression Statements

Any expression can be a statement:

x + 1
func_call()
obj.method()

Block Statements

{
    let x = 10
    let y = 20
    x + y
}

Return Statements

fn greet() str {
    return "Hello"     // explicit return
}

fn add(a int, b int) int {
    a + b              // implicit return (last expression)
}

Reply Statements (Plan 124)

Used in task message handlers for ask/reply RPC:

task CounterTask {
    on {
        GetCount() -> {
            reply self.count    // send reply to caller
        }
    }
}

Break Statements

for i in 0..100 {
    if i == 42 {
        break
    }
}

Import Statements

Needs modules

This example depends on multi-file modules and cannot run inline — open it in the Playground

use math::add           // import from module
use pac.db              // import from package root
use super.utils         // import from parent directory
use db: load, save      // import specific symbols
dep database(path: "../database")  // declare dependency

Type Declaration Statements

type Point { x int, y int }
enum Color { Red, Green, Blue }
tag Shape { Circle float, Rect int, int }
spec Printable { fn print() }
alias UserID = int

Extension Statements

ext str {
    fn is_empty() bool { self.len() == 0 }
}

Comment Statements

// Single-line comment
/// Doc comment
/* Block comment */

Empty Lines

Empty lines are preserved as statement separators for code formatting.

---

Control Flow

If Statements

// Basic if
if x > 0 {
    print("positive")
}

// If-else
if x > 0 {
    print("positive")
} else {
    print("non-positive")
}

// If-else if-else
if x > 0 {
    print("positive")
} else if x < 0 {
    print("negative")
} else {
    print("zero")
}

// If expression (value-producing)
let result = if x > 0 { 1 } else { 0 }

For Loops

// Range iteration (exclusive)
for i in 0..5 {
    print(i)    // 0, 1, 2, 3, 4
}

// Range iteration (inclusive)
for i in 0..=5 {
    print(i)    // 0, 1, 2, 3, 4, 5
}

// Array iteration
for item in [1, 2, 3] {
    print(item)
}

// With index
for i, item in [1, 2, 3] {
    print(f"${i}: ${item}")
}

// Condition loop (replaces while)
for i < 10 {
    print(i)
    i += 1
}

Note: Auto does not have a while keyword. Use for condition { } instead.

Loop Control

loop {
    if condition {
        break
    }
}

Pattern Matching (is expression)

is value {
    42 -> print("exact match"),
    as str -> print("string type"),
    in 0..9 -> print("single digit"),
    if value > 10 -> print("big number"),
    else -> print("other")
}

Note: Pattern branches use -> (arrow). Closures use => (double arrow).

Struct Destructuring (Plan 165)

let point = Point(10, 20)

is point {
    Point(x, y) -> print(f"x=${x}, y=${y}"),
    else -> print("not a point")
}

Option Pattern Matching (Plan 120)

is maybe_value {
    Some(x) -> print(f"got: ${x}"),
    None -> print("nothing")
}

Result Pattern Matching (Plan 120)

is result {
    Ok(value) -> print(f"success: ${value}"),
    Err(msg) -> print(f"error: ${msg}")
}

---

Functions

Function Definition

// Basic function (no return type annotation needed for void)
fn greet(name str) {
    print(f"Hello, $name!")
}

// Function with return type (space-separated, no ->)
fn add(a int, b int) int {
    a + b    // Implicit return (last expression)
}

// Function with explicit return
fn multiply(a int, b int) int {
    return a * b
}

// Function with no return value
fn print_message(msg str) void {
    print(msg)
}

Function Calls

greet("World")

let result = add(1, 2)

Generic Functions (Plan 048)

fn identity<T>(x T) T {
    x
}

fn first<T>(arr []T) ?T {
    if arr.len() == 0 {
        return None
    }
    Some(arr[0])
}

// With type constraints
fn compare<T has Comparable>(a T, b T) int {
    a.compare(b)
}

Parameter Modes (Plan 088)

Auto uses three parameter passing modes. The default is view (immutable reference).

// view - immutable reference (DEFAULT, O(1))
fn process(x int) {
    // x is an immutable reference
    // cannot modify x
}

// mut - mutable reference (O(1))
fn increment(x mut int) {
    x += 1    // modifies caller's value
}

// move - ownership transfer (O(1))
fn consume(data String) {
    // data is moved from caller
    // caller can no longer use data
}

The ParamMode enum supports: View (default), Mut, Move, Copy (deprecated), Take (deprecated, use Move).

Static Methods (Plan 035)

type Point {
    x int
    y int

    // Static method (called on type)
    static fn new(x int, y int) Point {
        Point(x, y)
    }

    // Instance method (called on instance)
    fn distance_to(other Point) float {
        let dx = self.x - other.x
        let dy = self.y - other.y
        (dx * dx + dy * dy).to(float).sqrt()
    }
}

let p = Point.new(3, 4)       // static call
let d = p.distance_to(p)      // instance call

Public Visibility (Plan 163)

pub fn public_function() int { 42 }

pub type Point { x int, y int }

pub enum Color { Red, Green, Blue }

pub spec Printable { fn print() }

Closures (Plan 060)

Closures use => syntax:

// Simple closure
let add = (a, b) => a + b
add(3, 4)    // 7

// Single-parameter closure (no parens needed)
let double = x => x * 2

// Typed closure with block body
let transform = (x int, y int) => int {
    let sum = x + y
    sum * 2
}

Capture semantics:

• By default, closures capture by reference (view)
• Use .move on the closure to capture by value

Function Annotations

#[vm]
fn vm_function(x int) void           // VM-implemented

#[c]
fn c_function(s str) int             // C-transpiled

#[c, vm]
fn hybrid_function(data []byte) void // both backends

Function Kinds

The FnKind enum supports 5 function types:

Kind	Description
Function	Regular function
Lambda	Lambda/anonymous function
Method	Instance method (associated with a type)
CFunction	C function declaration
VmFunction	VM-implemented function

Default Parameters

fn greet(name str, greeting str = "Hello") str {
    f"$greeting, $name!"
}

greet("World")               // "Hello, World!"
greet("World", "Hi")         // "Hi, World!"

Mutable Methods (Plan 163)

type Counter {
    count int

    mut fn increment() {
        self.count += 1
    }
}

var c = Counter(0)
c.increment()    // c.count is now 1

---

Data Structures

Arrays

// Array literal
let arr = [1, 2, 3, 4, 5]

// Index access
let first = arr[0]       // 1
let last = arr[-1]       // 5

// Slicing
let slice = arr[1..3]    // [2, 3]
let slice2 = arr[..4]    // [1, 2, 3, 4]
let slice3 = arr[3..]    // [4, 5]
let slice4 = arr[..]     // [1, 2, 3, 4, 5]

// Modification
var arr = [1, 2, 3]
arr[0] = 10    // [10, 2, 3]

Objects/Maps

// Object literal
let obj = {
    name: "John",
    age: 30,
    active: true
}

// Access members
print(obj.name)

// Modify members
obj.name = "Tom"

// Methods
obj.keys()           // ["name", "age", "active"]
obj.values()         // ["John", 30, true]
obj.items()          // [("name", "John"), ("age", 30), ("active", true)]

// Safe access
obj.get("name", "Unknown")
obj.get_or_insert("name", 10)

// Iteration
for k, v in obj {
    print(f"${k}: ${v}")
}

// Remove key
obj.remove("name")

Grid (2D Arrays)

// Grid definition
let grid = grid(a:"first", b:"second", c:"third") {
    [1, 2, 3]
    [4, 5, 6]
    [7, 8, 9]
}

// Convert to JSON
let json = grid.to_json()

---

Type Definitions

Type Definitions

Use the type keyword to define custom types:

type Point {
    x int
    y int
}

type Rectangle {
    top_left Point
    bottom_right Point
}

// Using custom types
let p Point = Point(10, 20)
let rect Rectangle = Rectangle(
    top_left: Point(0, 0),
    bottom_right: Point(100, 100)
)

Single Inheritance

type Animal {
    name str
    fn speak() str
}

type Dog is Animal {
    breed str
    fn speak() str { "Woof!" }
}

Generic Types (Plan 048)

type Container<T> {
    value T

    static fn new(value T) Container<T> {
        Container(value)
    }

    fn get() T {
        self.value
    }
}

// Const generics
type Inline<T, N u32> {
    data [N]T
}

Spec Implementation

type Point has Printable {
    x int
    y int

    fn print() {
        print(f"(${self.x}, ${self.y})")
    }
}

// Multiple spec implementations
type File has Readable, Writable {
    path str
}

Extension Blocks (ext)

// Add methods to existing types
ext str {
    fn is_empty() bool { self.len() == 0 }
    fn reversed() str { /* ... */ }
}

// With generic params (Plan 059)
ext<T> Vec<T> {
    fn first() ?T { /* ... */ }
}

Type Aliases

Create type aliases with alias:

alias UserID = int
alias Name = str
alias Coordinate = float

let uid UserID = 12345
let name Name = "Alice"
let coord Coordinate = 45.5

TypeDecl Fields

The TypeDecl struct in ast/types.rs includes:

Field	Type	Description
name	Name	Type name
parent	Option<Box<Type>>	Parent type (inheritance)
has	Vec<Type>	Spec implementations (has)
spec_impls	Vec<SpecImpl>	Spec implementations with type args
generic_params	Vec<GenericParam>	Generic type/const parameters
members	Vec<Member>	Data fields
methods	Vec<Fn>	Methods
attrs	Vec<AutoStr>	Annotations
is_pub	bool	Public visibility

---

Enums

Auto supports three enum kinds (from ast/enums.rs EnumKind).

Scalar Enums (C-style)

Simple enumeration with optional explicit values and repr type:

enum Color { Red, Green, Blue }

// With explicit values
enum HttpStatus u16 {
    OK = 200,
    NotFound = 404,
    ServerError = 500
}

Homogeneous Enums

All variants share the same payload type:

type Point { x int, y int }

enum Vertex Point {
    LeftTop
    RightTop
    LeftBottom
    RightBottom
}

Heterogeneous Enums (ADT / Sum Types)

Each variant can have a different payload type:

enum Msg {
    Quit,
    Move Point,
    Write str,
    Color(int, int, int)
}

Generic Enums

enum Option<T> {
    Some(T),
    None
}

enum Result<T, E> {
    Ok(T),
    Err(E)
}

EnumDecl Fields

The EnumDecl struct includes:

Field	Type	Description
name	AutoStr	Enum name
items	Vec<EnumItem>	Variants
kind	EnumKind	Scalar, Homogeneous, or Heterogeneous
is_pub	bool	Public visibility

Tags (Tagged Unions)

Tags provide type-safe discriminated unions (similar to Rust enums):

tag MyTag {
    i int
    f float
    c char
}

let value MyTag = MyTag.i(42)

// Pattern matching with `is`
is value {
    i -> print("int"),
    f -> print("float"),
    c -> print("char")
}

---

Specs (Traits)

Specs define interface-like contracts that types can implement (Plans 019, 057, 059).

Spec Declaration

spec Printable {
    fn print() void
}

spec Readable {
    fn read(buf []byte) int
}

Generic Specs

spec Iterable<T> {
    fn iterator() Iterator<T>
}

spec Comparable<T> {
    fn compare(other T) int
}

Default Methods

spec Loggable {
    fn log_level() str { "info" }
    fn log(msg str) void {
        print(f"[${self.log_level()}] $msg")
    }
}

Spec Implementation

type User has Printable {
    name str

    fn print() void {
        print(self.name)
    }
}

SpecDecl Fields

The SpecDecl struct includes:

Field	Type	Description
name	Name	Spec name
generic_params	Vec<GenericParam>	Generic parameters
methods	Vec<SpecMethod>	Required/default methods
is_pub	bool	Public visibility

Transpilation Behavior

• C backend: Specs transpile to vtables (struct of function pointers)
• Rust backend: Specs transpile to native Rust traits
• VM mode: Specs use dynamic dispatch via method registry

---

Generics

Auto supports generics with type parameters and const parameters (Plan 048).

Type Parameters

type Container<T> {
    value T
}

fn identity<T>(x T) T { x }

Const Parameters

type Inline<T, N u32> {
    data [N]T
}

let buffer Inline<int, 64> = Inline.new()

Generic Constraints

fn sort<T has Comparable>(items []T) []T {
    // T must implement Comparable spec
}

Monomorphization

Generic types and functions are monomorphized at compile time for C/Rust backends, generating specialized code for each concrete type instantiation.

---

Closures

Auto closures use => syntax (Plan 060).

Syntax Forms

// No params
let thunk = => doSomething()

// Single param (no parens)
let double = x => x * 2

// Multiple params
let add = (a, b) => a + b

// Typed params
let multiply = (a int, b int) => int { a * b }

Capture Semantics

let x = 10

// Captures x by reference (view)
let closure = () => x + 1

// Captures x by value (move)
let moved = () => x + 1 .move

Iterator Usage

let nums = [1, 2, 3, 4, 5]
let doubled = nums.map(x => x * 2)
let evens = nums.filter(x => x % 2 == 0)

---

Option and Result

Auto provides ?T (Option) and !T (Result) for error handling (Plan 120).

Option (?T)

let name ?str = Some("Alice")
let empty ?str = None

// Pattern matching
is name {
    Some(n) -> print(f"Hello, $n"),
    None -> print("no name")
}

// Null coalescing
let display = name ?? "unknown"

Result (!T)

fn divide(a int, b int) !int {
    if b == 0 {
        return Err("division by zero")
    }
    Ok(a / b)
}

// Error propagation with .?
let result = divide(10, 0).?    // propagates Err

// Pattern matching
is result {
    Ok(value) -> print(value),
    Err(msg) -> print(f"Error: $msg")
}

Constructors

Constructor	Type	Description
Some(value)	Option	Wrap a value
None	Option	No value
Ok(value)	Result	Success
Err(message)	Result	Failure

---

Concurrency: Tasks and Async

Auto provides an Actor-based concurrency model (Plans 121, 124, 126).

Task Definition

task CounterTask {
    count int = 0

    start() {
        print("Counter started")
    }

    on {
        Increment(n int) -> {
            self.count += n
        }
        GetCount() -> {
            reply self.count
        }
        Reset -> {
            self.count = 0
        }
        _ -> {
            print("unknown message")
        }
    }

    stop() {
        print(f"Counter stopped at ${self.count}")
    }
}

Task Attributes

#[single]
task UniqueTask {
    on { /* ... */ }
}

Spawning and Communication

let handle Handle<CounterTask> = spawn CounterTask()
handle.send(Increment(5))
handle.send(GetCount)    // for ask/reply

Message Patterns

Pattern	Syntax	Description
Simple	Reset	No data
With bindings	Add(val)	With named bindings
Literal match	"start"	Exact literal match
Type binding	msg str	Capture by type

Async / Await (Plan 124)

// Async function (~T return type)
fn fetch_data(url str) ~str {
    // ~T indicates async return
    let response = http_get(url).await
    response.body
}

// Async block
let result = ~{
    let a = fetch_data("/api/a").await
    let b = fetch_data("/api/b").await
    a + b
}

Background Execution (Plan 126)

// .go spawns to background worker pool
let handle = compute_heavy(data).go
// ... do other work ...
let result = handle.await

---

Compile-Time Metaprogramming

Auto supports compile-time code execution (Plan 095).

#if — Compile-Time Conditional

#if DEBUG {
    print("debug mode")
} else {
    print("release mode")
}

#for — Compile-Time Loop Unrolling

#for i in 0..4 {
    let bit_${i} = 1 << i
}
// Generates: let bit_0 = 1, bit_1 = 2, bit_2 = 4, bit_3 = 8

#is — Compile-Time Pattern Match

#is target_os {
    "linux" -> { const PLATFORM = "linux" },
    "windows" -> { const PLATFORM = "windows" },
    else -> { const PLATFORM = "unknown" }
}

#{} — Compile-Time Expression

const SIZE = #{ 1024 * 768 }

---

Ownership and Borrowing

Auto implements the "Trinity of Resources": view, mut, move (Plan 122).

Access Modes

Mode	Syntax	Cost	Description
view	x.view	O(1)	Immutable borrow (&T)
mut	x.mut	O(1)	Mutable borrow (&mut T)
move	x.move	O(1)	Ownership transfer
clone	x.clone()	O(N)	Deep copy

Default Parameter Mode

Function parameters default to view (immutable reference):

fn process(data str) {
    // data is borrowed immutably (view mode)
    print(data)
}

Ownership Transfer

fn consume(s String) {
    // s is moved; caller no longer has access
    print(s)
}

let text = String.new("hello")
consume(text.move)
// text is no longer accessible here

Hold

let val = expr.hold    // extend lifetime binding

---

Modules and Imports

Auto supports a hierarchical module system (Plan 131).

Import Syntax

Needs modules

This example depends on multi-file modules and cannot run inline — open it in the Playground

use db              // Same directory: ./db.at or ./db/mod.at
use super.db         // Parent directory: ../db.at
use pac.db           // Package root: search source dirs
use pac.api.handlers // Deep path from root
use db: load, save   // Import specific symbols

Dependency Declaration

// In pac.at
name: "myapp"
src: ["src"]
dep database(path: "../database")

Public Exports

pub fn public_function() int { 42 }
pub type Point { x int, y int }
pub use math::add

Resolution Rules

1. Try name.at (file module)
2. Try name/mod.at (directory module)
3. Error if both exist (ambiguous)
4. Error if neither exists

---

UI Widgets and Routing

Widget Declaration (Plan 096)

widget CounterView {
    model {
        count int = 0
    }

    msg {
        Increment
        Decrement
    }

    view {
        col {
            text(text: f"Count: ${model.count}")
            button(text: "+") {
                onclick: emit Increment
            }
            button(text: "-") {
                onclick: emit Decrement
            }
        }
    }
}

Routing (Plan 105)

routes {
    route("/", HomeView)
    route("/about", AboutView)
    route("/users", UserListView)
}

// Navigation
nav("/about")
link(text: "Go to About", to: "/about")

// Outlet for nested routes
outlet()

---

Nodes

Nodes are Auto's XML-like tree structure for data representation, combining JSON's simplicity with XML's hierarchical nature. Auto can be compiled down to Atom format.

Basic Node Syntax

node_name(a: 1, b: "hello") {
    // children
    sub_node(c: 2) {
        // ...
    }

    // children
    sub_node2() {
        // ...
    }
}

这个结构和XML的树状结构基本一致，例如，上面的代码用XML可以表示为：

<node_name a="1" b="hello">
    <sub_node c="2">
        <!-- more content -->
    </sub_node>
    <sub_node2>
        <!-- more content -->
    </sub_node2>
</node_name>

可以看到，这里节点名称，属性参数（在XML中叫attribute）和子节点的定义， 信息量上是完全对等的。

相比于XML，Auto的节点定义格式有如下优点：

1. 更加紧凑，没有冗余的尖括号和结束标签。
2. 形式上更接近于C系列语言的风格，可以和其他Auto代码良好地融合在一起
3. 还有简化空间。

Simplifications to node syntax

当某个节点没有属性时，可以省略括号：

root {
    // subnodes
}

当节点没有子节点时，可以省略掉{..}：

leaf(id: "my_leaf")

此时，节点的定义从语法上就和函数调用基本一致了，从语法上来看，产生了歧义。

Auto语言从语义上来解决这个歧义：

1. 节点的定义其实也是一种函数调用，相当于一个构造函数
2. 节点的名称如果定义为fn，则这个表达式是函数调用；如果是一个类型type，则为该类型的构造函数。

这样设计的话，节点表达式和类型的实例化就统一起来了。

当节点的定义很明确时，我们可以忽略掉属性的名字，直接调用参数值：

type Point {
    x int
    y int
}

let p = Point(10, 20)

如果节点的类型本身有一个主属性（一般是id或name）， 那么可以用节点声明表达式来定义一个实体：

type User {
    @primary
    name str

    age int
}

User XiaoMing {
    age: 18
}

// 相当于：
let XiaoMing = User(name: "Xiaoming", age: 18)

这种方式可以直接定义一个变量，在结构化的配置文件中很好用。

Examples

// Simple node
root(id: "123") {
    name("Puming")
    age(41)
}

// Nested nodes
root(id: "123") {
    name("Puming") {
        surname("Zhao") {
            // More nested content
        }
    }
    age(41)
}

Node vs Object

In Auto, object is actually a subset of node.

You can view object as a special type of node that is:

1. Anonymous: the node type is not specified, or actally put as an property inside the {}
2. Single: no directy sub-nodes are specified, i.e. subnodes are specifed as properity values.

Object (data):

let obj = {
    name: "value",
    count: 42
}

Node (structure):

node(attr: "value") {
    child()
}

Key differences:

• Nodes use () for attributes, {} for children
• Nodes represent tree structures (like XML)
• Objects represent key-value mappings (like JSON)

Use Cases

Nodes are commonly used in:

1. UI Description (AutoUI):

window(title: "My App") {
    button(label: "Click me") {
        onclick: => print("clicked")
    }
    textbox(placeholder: "Enter text")
}

2. Configuration (AutoConfig):

config(version: "1.0") {
    database(host: "localhost", port: 5432) {
        credentials(user: "admin", pass: "secret")
    }
}

3. Code Generation (AutoGen):

for student in students {
    student(name: student.name, age: student.age) {
        for course in student.courses {
            course(name: course.name, score: course.score)
        }
    }
}

Node Compilation

Dynamic Auto code compiles to static Atom:

Input (Auto):

var name = "Puming"
root(id: "123") {
    name(name)
    age(41)
}

Output (Atom):

root(id: "123") {
    name("Puming")
    age(41)
}

---

Memory Management

Storage Lifetimes

Auto supports multiple memory lifetimes:

Lifetime	Description
Immortal	Persists beyond program end
Process	Program lifetime (globals)
Auto	GC/RC managed
Task	Task completion
Scope	Function/block scope
Instant	Statement-level

Memory Management Strategies

Auto provides three memory management strategies:

1. Manual (C-like): Explicit allocation/deallocation
2. Automatic (GC): Garbage collected
3. Automatic (RC): Reference counted

---

Implementation Comparison

C Implementation vs Rust Implementation

Feature Completeness

Feature	Rust	C
Lexer	Complete	Complete
Parser	Complete	Partial
Evaluator	Complete	Partial
Transpilation	Complete	Not implemented
Type System	Complete	Partial
Pattern Matching	Complete	Not implemented
F-Strings	Complete	Complete

---

Appendices

Appendix A: Operator Precedence (Highest to Lowest)

Level	Operators	Associativity
1 (highest)	.view, .mut, .move, .await, .go, .hold	Left
2	! (NOT), - (negate)	Right
3	*, /, %	Left
4	+, -	Left
5	<, >, <=, >=	Left
6	==, !=	Left
7	&&, and	Left
8	`
9	??	Left
10	.., ..=	Left
11 (lowest)	=, +=, -=, *=, /=, %=	Right

Appendix B: Reserved Keywords (55 keywords)

alias, and, as, await, break, const, copy, dep, else, enum, Err, ext,
fn, for, go, grid, has, hold, if, impl, in, is, let, link, route,
nav, move, mut, nil, node, None, null, Ok, on, or, outlet, pac,
pub, reply, routes, shared, Some, spec, spawn, static, super, tag,
task, to, true, false, type, union, use, var, view

Appendix C: Expression Types (55 variants from ast.rs)

Int, Uint, I8, U8, I64, U64, Byte, Float, Double, Bool, Char, Str,
CStr, Ident, GenName, Ref, View, Mut, Move, Take, Hold, Unary, Bina,
Dot, Range, Array, Pair, Block, Object, Call, Node, Index, Lambda,
Closure, FStr, Grid, Cover, Uncover, OptionPattern, ResultPattern,
OptionUncover, ResultUncover, StructPattern, If, Nil, Null,
NullCoalesce, ErrorPropagate, Cast, To, Some, None, Ok, Err,
BoxExpr, ArcExpr, NavCall, AsyncBlock, Await, Go, Comptime

---

Document Version: 0.2-draft Status: Work in Progress Feedback: Please report issues and suggest improvements via GitHub issues or pull requests.