Logical operators

Logical operators are used to compare values, combine conditions, and test membership.

Truthiness

In if and other conditional contexts, these values are falsy:

• false
• null
• 0
• "" (empty string)
• empty collections
• errors

Everything else is truthy.

For optional collections, strings, numbers or boolans, use is not null when you want to accept falsy values but reject null.

let users: Array(User)?

if users is not null {
  -- users can still be an empty array here
}

if user {
  -- user is truthy (not null)
}

if not isEnabled {
  -- runs when isEnabled is false or null
}

Equality and type checks

Use is to check value equality or type membership.

if status is "ready" {
  start()
}

if value is Animal {
  feed(value)
}

Use is not or is no to negate an is check.

if user is not null {
  console.log(user.name)
}

Use == and != for direct value equality and inequality.

assert(score == 42)
assert(score != 0)

let animal = Animal()

assert(animal is Animal) -- works, animal is an instance of Animal
assert(animal == Animal) -- does not work, animal does not equal Animal

Negation

not and no have the same effect and negate a value.

if not hasPermission {
  deny()
}

if no items {
  console.log("empty")
}

Boolean logic

Use and and or to combine conditions.

if isLoggedIn and isAdmin {
  showPanel()
}

if isPreview or isDebug {
  enableVerboseLogs()
}

Membership

Use is in to check if a value is contained in a collection.

if userId is in allowedIds {
  allow()
}

Use is not in to negate membership.

if role is not in ["admin", "moderator"] {
  deny()
}

Comparisons

Comparison operators are >, >=, <, <=. They can be chained.

if 2 < a < 12 {
  console.log("in range")
}