Language specification (1.0 development)

Lexical rules

UTF-8 source is tracked with byte-accurate spans; whitespace and indentation have no semantic meaning. Python-style # line comments are preferred. // and /* ... */ remain accepted. Blocks use {} and ordinary statements end with ;. Identifiers begin with an ASCII letter or _. String literals use double quotes and character literals use single quotes.

Bindings and types

var creates a mutable, type-locked binding. const creates an immutable binding. A type is inferred from an initializer unless written after :. any is the explicit dynamic escape hatch. The built-ins are int, float, num, str, char, bool, null, void, and any; int and float are distinct and both are compatible with num. Types are non-nullable by default; T? is sugar for T | null. The legacy spellings let, set, and func remain accepted as aliases of var, const, and fn.

1var count: int = 1;
2const title = "Kyna";
3var maybe: str? = null;

Objects are closed: an assignment to a field not present in the object/class shape is rejected by the runtime. Arrays use [a, b], zero-based integer indexing, and are mutable reference values; len, push, and pop are standard-library operations. null is a value and void describes absence of a function result.

Functions and control flow

Parameters always have types and calls always use parentheses. Return annotations are optional for safely inferred functions and mandatory contracts when present. if requires a parenthesized condition and braced branches and supports else if chains. while and loop (init; condition; increment) are statements. break and continue may name a loop label. switch selects among constant case values: each arm is case VALUE: { ... }, the optional default arm must come last, and control does not fall through. await expr is a unary prefix operator that binds a pending result (currently a synchronous pass-through that lets await fetch(...) style code read naturally; see examples/language/await_and_network.kyna). match currently accepts literal and _ arms; arms use => and terminate with ;. throw value; raises a typed Error; non-Error values become an Error whose cause is the original value. catch (failure) receives that Error and may inspect failure.code, failure.message, and failure.cause. finally runs on normal completion, return, caught failure, and rethrow.

VM-generated failures use the same exception path and are catchable. if is expression-capable; loops are not.

Objects and classes

Class inheritance is single-parent. Constructors are named init, construction uses new, and instance access requires explicit self. super.member resolves a parent member. Unmodified members are private. protected is visible to subclasses and public is visible everywhere. Static and instance access are distinct. Overrides require override, cannot narrow visibility, and must preserve parameter and return contracts. Final classes/methods cannot be extended/overridden. Abstract signatures end in ;; concrete classes must resolve all abstract methods.

intf declares a structural shape. Classes opt in with implements A, B; closed object values are checked structurally when used as interface values. Imports create immutable namespaces and expose only declarations explicitly marked export. Nested functions are lexical closures: captured bindings remain alive after their declaring call returns, mutable captures are shared by cell, and separate closure factories produce independent state. Traits, generics, richer patterns, and streaming/async networking remain future work.