void doublePrint(int n) {
    IO.println(n * 2);
}

void main() {
    int a = doublePrint(5);
    IO.println("a is " + a);
}

// From Groundwork, chapter 6 (ch06-methods), box 7.
// This example is from Groundwork, licensed CC BY-NC-SA 4.0.
// Run with: java ch06_07.java
// This fails on purpose: it does not compile—A void method's result stored in a variable, which javac refuses. The error message is the lesson.