Variables and Bindings

AetherShell supports several forms for declaring and binding variables, from explicit let declarations to concise shorthand syntax.

Let Bindings

The standard way to declare a variable:

let name = "AetherShell"
let version = 3
let features = ["typed", "pipelines", "AI"]

Variables are immutable by default. Attempting to reassign an immutable variable produces an error:

let x = 10
x = 20    # Error: Cannot reassign immutable variable 'x'. Use 'let mut x' to make it mutable.

Mutable Variables

Use mut to allow reassignment:

let mut counter = 0
counter = counter + 1    # OK
counter = 42             # OK

Or with shorthand:

mut counter = 0
counter = counter + 1

Shorthand Syntax

AetherShell offers shorter forms for common patterns:

# These are all equivalent:
let x = 10
x = 10       # Inferred let
x := 10      # Walrus-style binding

Public Variables

Variables can be marked public for export from modules:

pub let API_URL = "https://api.example.com"
pub let VERSION = "1.0.0"

Public variables are accessible when the module is imported.

Type Annotations

Optional type annotations can be added to bindings:

let name: String = "hello"
let count: Int = 42

Type annotations are parsed but currently used for documentation purposes. The type inference engine (typecheck.rs) handles type validation.

Scoping Rules

AetherShell uses a flat environment model:

• All variables share a single scope
• Lambda parameters are temporarily bound during execution and restored after
• There are no block-level scopes or shadowing in the traditional sense
• Variables are visible once declared and remain available for the rest of the session

let x = 10
let f = fn(x) => x * 2    # Lambda parameter 'x' temporarily shadows outer 'x'
f(5)                        # => 10
x                           # => 10 (outer x unchanged)

Environment Variables

Shell environment variables are accessible and can be set:

# Access environment variable
let home = $HOME

# Set environment variable
export PATH = "/usr/local/bin:${$PATH}"

Assignment vs. Declaration