Values and variables

Bindings introduce named values. val is immutable, var is mutable, and both require an explicit type - mach has no type inference.

Declaring bindings

A binding names a value with a declared type. val is constant once set; var can be reassigned. Every form pins the type in the declaration.

val NAME: TYPE = EXPR;              # immutable; initializer required
var NAME: TYPE;                     # mutable; default-initialized
var NAME: TYPE = EXPR;              # mutable; explicit initializer

Mutability and defaults

A val always carries an initializer and cannot be reassigned. A var may omit its initializer, in which case it is default-initialized (zeroed), and it can be written to afterward.

val pi: f64 = 3.14159;
val n:  i64 = 42;

var counter: i64 = 0;
var buf:     [256]u8;               # default-initialized to zero

counter = counter + 1;              # var is reassignable

Scope and exports

Both forms work at module top level and inside function bodies. Inside a function, a binding is local to its enclosing block. At module top level, pub exports it:

• pub val NAME exports the constant.
• pub var NAME exports the variable as a writable global.

No type inference

Every binding declares its type. An untyped numeric literal is checked against the binding's declared type; it never participates in inferring that type.

val n: i64 = 42;                    # ok - 42 conforms to i64
val x      = 42;                    # ERROR - no type to check against