Booleans

Calibre uses bool for values that are either true or false.

let open : bool = true;
let locked := false;

Booleans are commonly produced by comparisons.

let a := 10;
let b := 20;

print(a < b); // true
print(a = b); // false
print(a != b); // true

You can combine boolean expressions with &&, ||, and !.

let age := 20;
let mut has_ticket := false;


// true - `!` inverses the value of the bool
has_ticket := !has_ticket

// true - `&&` represents `and` therefore is only true when both its inputs are true
let can_enter := age >= 18 && has_ticket;

// false - `||` represents `or` therefore is only true when one of its inputs are true
let needs_help := !has_ticket || age < 18;

Booleans are often used with if expressions.

const can_vote := fn (age : int) -> bool => age >= 18;

const main := fn => {
  if can_vote(21) => print("allowed") else => print("not allowed");
};

Many standard library functions also return booleans, such as "calibre".starts_with("cal") or list:<int>[1, 2, 3].contains(2).