Expression Syntax

Basic forms

Expression := Literal
            | Identifier
            | MemberAccess
            | Call
            | Index
            | UnaryExpression
            | BinaryExpression
            | IfExpression
            | ForExpression
            | SwitchExpression

Members, calls, and indexing

Point point = Point(x: 2, y: 4)
Integer x = point.x
String first = names[0]

Multiparameter calls use name: value. A single argument may omit its name; in a multiparameter call, a bare identifier may omit its label if it has the same name as the matching parameter. Other positional arguments are invalid, while named arguments may appear in any order. Receivers, arguments, and indices evaluate once in source order. Safe navigation, implicit await, and dynamic member lookup are not part of this grammar.

Operations

Integer total = base + quantity * price
Boolean accepted = ready && total > 0

Operators are fixed and cannot be overloaded. Logical operations accept Boolean only and short-circuit. Assignment is a separate statement and produces no value for a larger expression.

throw may appear in an expression position expecting a value. Its operand must be a non-null Exception. It produces no value, following the same propagation and catch/finally rules as a throw statement; the surrounding expected type determines its result type.

var todo = repository.findById(id) ?? throw Exception(message: "任务已不存在")

?? evaluates its right side only when the left side is null. After a successful query in this example, todo has a non-null type and no exception is created. The query expression runs only once.

If expressions

String state = if active {
    "active"
} else {
    "inactive"
}

The condition must be Boolean. Branches produce results through a trailing expression or explicit break value. Every normally completing path must yield a value; return in a branch still exits the surrounding function. Branches retain ordinary if type narrowing and local scope.

Braces may be omitted for a branch containing only one result expression: if editing "" else task.title. This does not depend on newline placement. Branches with declarations, assignments, or several statements still use braces. An else belongs to the nearest unmatched if.

Parentheses around a condition mark its end clearly, as in if (ready) -1 else 0. Without them, the condition follows ordinary expression parsing. If a branch starts with a minus sign, parenthesis, or another symbol that might continue the condition, parenthesize the whole condition or retain branch braces.

For expressions

Integer found = for Integer number : numbers {
    if number > 0 { break number }
} else {
    break 0
}

Switch expressions

String text = switch token {
    case Name(String value) { break value }
    case End { break "end" }
}

Every possibly normally completing path of a control-flow expression must produce a compatible value; null is not inserted implicitly. See advanced function rules for trailing-return behavior in callable bodies.