Let Bindings

In Rue, everything is immutable. This means there isn't the traditional concept of a mutable variable whose value can be reassigned. Once a value is given to a variable, it's final unless you make a new variable.

Here's an example:

fun main() -> Int {
    let num = 42;
    num + 10
}

This will bind num to the value 42, then add it to 10 and return the result.

note

This is not possible, since it's immutable:

fun main() -> Int {
    let num = 42;
    num = 34; // You can't assign to bindings.
    num + 10
}

What's the point?

Bindings let you prevent repetition and optimize code when a value is used more than once. It can also be used to make code clearer.

For example, we use num twice in this example, but it only needs to be written once, both in the code and in the compiled output:

fun main() -> Int {
    let num = 42;
    num * num
}

If a binding is only used once, it will be inlined as though you wrote the value directly.