Operators and Expressions

Precedence, arithmetic semantics, optional operators, casts, assignment, and expression values.

Expression model

Most constructs that compute a value can appear wherever a value is expected.

La3 uses expressions to keep examples direct. A block can return its final expression, if can choose a value, match can compute a result, and loop can finish with break value. The reader sees data flow instead of a trail of mutable temporaries.

Statements are still available where a value is not needed.
An early return is allowed and should be used for guard clauses.
Branches that produce values must agree on type.
The type checker treats expression value and control-flow reachability as one semantic unit.

Arithmetic semantics

Numeric operators have explicit, documented behaviour so examples do not depend on host-language guesses.

Integer / truncates toward zero.
% keeps the sign of the left operand.
// is floor division.
** always produces f64 because exponentiation naturally escapes integer-only results.
Mixed numeric arithmetic requires an explicit as cast.

let a = 7 / 2        // 3
let b = -7 / 2       // -3
let c = -7 // 2      // -4
let d = 2 ** 10      // f64

Logical operators

&&, ||, and ! are boolean operators, not value-selection operators.

La3 deliberately avoids the Lua convention where logical operators return one of their operands. That idiom is compact, but in a language that otherwise resembles Rust, C, and TypeScript it would make familiar syntax mean something surprising.

&& evaluates the right side only when the left side is true.
|| evaluates the right side only when the left side is false.
Both operators always produce bool.
Use ?? for value defaults and ?. for optional access.

Optional operators

?? and ?. are the lightweight control-flow operators for T | nil.

left ?? right evaluates right only when left is nil.
receiver?.field returns nil when receiver is absent.
Chained optional access short-circuits at the first absent link.
Option<T> has its own method vocabulary, including map, unwrap_or, and ?.

let port = opts.port ?? 443
let city = user?.address?.city ?? "unknown"

Casts

as marks every conversion that can change representation or lose information.

The checker accepts numeric-to-numeric casts and integer-to-char or char-to-integer casts. It rejects conversions that would pretend unrelated runtime representations are the same thing, such as a string cast directly to an integer.

Float-to-integer casts truncate.
Integer narrowing keeps the low bits of the value.
There is no implicit widening just because the destination type is larger.
The docs should show casts at protocol boundaries, binary formats, and size conversions.