Kairo Built-in Types and Collections Reference

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Scalar types

• Integer literals default to Int64. Assign to Int32 explicitly to narrow.
• Fractional literals default to Decimal. Float64 requires explicit typing or conversion.
• Overflow is a compile-time error when a literal cannot fit the target type.

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Literals

let count: Int64 = 100
let price: Decimal = 125.50
let message: Text = "Customer updated"
let active: Bool = true

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Nullable type T?

• T and T? are different types.
• null may only be assigned where the target type is nullable.
• Nested nullables like T?? are not part of v0.1.
• Inside a value, T? is allowed only when T is value-like.

public func findCustomer(id: CustomerId): Customer? {
    return null
}

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Collections

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List<T>

public value CustomerPage {
    ids: List<CustomerId>
}

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Set<T>

public value CustomerTags {
    tags: Set<Text>
}

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Map<K, V>

public value ExchangeRates {
    rates: Map<Text, Decimal>
}

• List<T> is value-like only when T is value-like.
• Set<T> is value-like only when T is value-like.
• Map<K, V> is value-like only when both K and V are value-like.

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Result<T, E>

• Part of the Kairo Core prelude; no import required.
• E must be value-like.
• Constructed with Result.success(value) or Result.failure(error).
• Contextually typed as Result<T, E> in v0.1.

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Generic type parameters

public contract Formatter<T> {
    func format(value: T): Text
}

• Type argument arity must match the declaration.
• Generic values may not store unconstrained generic parameters in value members in v0.1.

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Generic contract constraints

public contract Formatter<T: Displayable> {
    func format(value: T): Text
}

• Constraint target must resolve to a contract.
• Multiple constraints and non-contract constraints are deferred.

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Deferred

• Custom equality rules
• Mutable collections
• Broad numeric promotion
• Additional temporal types
• T: value and other non-contract constraints

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