Variables and Bindings

Cerune binds a name to a value. Each binding has a type determined when it is declared. Reassignment is not allowed by default. Add mut to allow reassignment with another value of the same type.

Declarations and reassignment

count: i64 = 40;
mut total: i64 = count;
total = total + 2;
print(total); // 42

Syntax	Meaning
`name: T = value;`	Declare a binding of type `T` that cannot be reassigned
`mut name: T = value;`	Declare a binding of type `T` that permits reassignment
`name = value;`	Reassign an existing `mut` binding

Do not repeat the type annotation when assigning to an existing binding. Assigning to a binding without mut is a type-checking error.

Type inference (infer)

infer determines the type from the declaration’s initializer. It does not make a binding dynamically typed.

mut value: infer = 1; // i64
value = 2;            // OK
// value = 0.5;       // type error: cannot assign f64

An integer literal with no contextual type defaults to i64, while a floating-point literal defaults to f64. Explicit type annotations or surrounding expressions can determine a literal’s type instead.

Cerune does not perform implicit numeric conversions. See Types and the primary source’s numeric literal rules.

Updating arrays and strings

A mut array binding permits element updates. Arrays have value-copy semantics, so an element update to one copy does not affect another.

The contents of a string value are immutable. A mut string binding can be reassigned to a different string but cannot be used to change part of the string in place.

Block scope

Braced blocks, including the bodies of if statements and loops, create new scopes.

A binding declared in a block is not available outside it.
Inner blocks can read outer bindings and reassign them if declared with mut.
Inner blocks may declare a distinct binding with the same name as an outer binding (shadowing).
Bindings declared by a for initializer are available in its condition, update, and body, but not after the loop.

Examples and primary sources

conditional.ceru — Reassignment of outer bindings and bindings inside branches
loop_control.ceru — mut bindings updated in loops
owned_arguments.ceru — Value copies and array updates
Language reference (primary source) — “Mutable bindings and reassignment” and “Conditionals, loops, and block scope”

This page is a summary. Consult the primary specification for exact evaluation-order, assignment, and scoping rules.