Variables
The let keyword is used to define a variable in MoonBit.
Type Annotation
You can specify the type of a variable by using a colon followed by the type name. Type annotation is optional - if not provided, MoonBit will automatically infer the type from the assigned value.
If you don't want to define an extra variable, you can also add a type annotation to any expression using the syntax (expression : Type).
Mutability
Variables in MoonBit are immutable by default, which means they cannot be reassigned after initialization. To create a mutable variable that can be reassigned, add the mut keyword before the variable name.
///|
fn main {
// explicit type annotation
let a1 : Int = 10
println((10 : Int))
// Variable with type inference (Int inferred from value 20)
let b = 20
println("a + b = \{a1 + b}")
// Mutable variable - can be modified
let mut c = 10
println("c before: \{c}")
c = c + 1
println("c after: \{c}")
// Immutable variable - cannot be modified
let d = 20
println("d = \{d}")
// d = d + 1 // Uncommenting this line will cause a compilation error
}