Assignments

Values might be assigned to a variable, where variables' names must start with a letter and can be followed by more letters, numbers, :, and _.

In Rust it is common to set a variable preceded by in let, however, that's not required in here, meaning both of these statements are correct:

let my_number = 5

my_number = 5

A value might be reassigned in the same fashion as in an assignment:

my_number = 5
my_number = 10

Using let allows you to just clarify ambiguity when working with nested blocks:

modify_me = "I am unmodified"
do_not_modify_me = "I am unmodified"
if true {
    modify_me = "Modified!" //This reassigns 'modify_me'
    let do_not_modify_me = "Assigned!" //This create a new variable 
                                       // only available on this scope
    print(modify_me) //Prints Modified!
    print(do_not_modify_me) //Prints Assigned!
}
print(modify_me) //Prints Modified!
print(do_not_modify_me) //Prints I am unmodified

Input variables

If you are not the developer of the program that is using MoonScript, you might find the developers used Input Variables, these are variables the developers include into your code without you requiring to use it.

For example, if the context of the program was a car rental, you might be writing a script for actions to take after an user has asked to rent a specific car, to allow you using them, the developer might give you variables like car, appointment, or client so you can access a bigger context, when they do, you don't need to do anything special, you can use them directly, like this:

println("Sending email to the client with rent details");
client.send_email("You have rented a car for the date "+appointment.date.to_string);

For more information about the Input Variables used by your program, contact its developers and their documentation.

Optimizations

Values and variables known at compile-time* might get inlined when possible:

a = 5
b = a
print(b)

print(5)

*This includes some of the Input Variables