Combining conditions

and, or, not, xor — written out in full, and only on bool values.

One question is rarely enough. Archon combines several with four words.

@entry(start)
object MyProgram {
    start() {
        var age := 42;
        var registered := true;

        if (age >= 18 and registered) {
            Console.print(text: "may vote");
        }

        if (not registered) {
            Console.print(text: "still to register");
        } else {
            Console.print(text: "already registered");
        }
    }
}

Four words, written out in full

There is no &&, no ||, no !: the logical operators are written the way they are read. The exclamation mark stays reserved for !=, and nothing else — which is what makes it recognisable at a glance.

xor is the least common of the four: it is true when the two answers differ. “One or the other, but not both.”

Only on bool values

Like the condition of an if, these four words accept nothing but bool values. age and registered is refused when age is a number — it takes a comparison, something that gives back an answer: age >= 18 and registered.

It is the same rule as in 3.2, one step further out, and for the same reason: a number is not an answer to a question.

Reading a compound condition

if (age >= 18 and registered) {

The comparison happens first, the and after — >= binds tighter than and, the way * binds tighter than + in arithmetic. So you do not have to bracket each comparison. Where a doubt remains, parentheses are allowed and make the intent explicit.

Your turn

• Set registered to false: the first condition falls, the second changes branch.
• Replace and with or and predict the output before running.
• Write if (age and registered) — with no comparison. The refusal names the type and expects, and says in its own way that a condition is built from answers, not from numbers.
• Try xor between registered and a second bool variable of your choosing, and check that it is false when both are true.