1. Functions

Every program in Serene is required to have a main function. Here is a basic example of a main function that prints "Hello world!" on a new line.

function main() {
    print "Hello world!"
}

In Serene, the body of a function is a sequence of statements, each beginning with a keyword. Let's define another function that takes a parameter and also returns a value. The invert function is pretty trivial, but it shows what a typical function signature looks like. Note that the types of both the parameters and return values must be specified.

function invert(b: Bool) -> Bool {
    return (not b)
}

function main() {
    run invert(True)            //return value is discarded
    print invert(True)          //return value is printed
}

Remember that the body of a function is a sequence of statements: invert(True) on its own isn't a statement, so we use the run keyword to execute it.