What are functions in Go and how do you define them?

A function is defined with the func keyword, then its name, its parameters and its result types.

• Parameters that share a type can share one type name, as in a, b int.
• A Go function can return multiple values, and the usual pattern returns a result plus an error last.
• Named return values act as local variables, and a bare return sends back their current values.
• Functions are also values, so you can pass them as arguments, store them in variables and return them as closures.

func add(a, b int) int {
    return a + b
}

func divide(a, b float64) (float64, error) {
    if b == 0 {
        return 0, errors.New("division by zero")
    }
    return a / b, nil
}
func calculate(a, b int) (sum, product int) {
    sum = a + b
    product = a * b
    return // naked return
}