Lyric

What changed in v1.13.0 — 2026-08-19

The language gaps close. Interface inheritance arrives — one parent, implied through the whole chain — compound assignment reaches through the operator interfaces, block lambdas infer their return type, and std.core becomes the import-free root of the library. One question got its documented No: heterogeneous operator arithmetic. The bytecode format stays 3.2.

Added

• Interface inheritance: an interface may declare one parent — interface Labeled :: [Named]. Conforming to the child implies conforming to the whole chain: implementing types provide the chain's abstract members (a missing one names the implying interface), inherit its default methods, satisfy parent constraints, and carry into parent-typed interface values. A value of the child's interface type answers the parent's members too. The rules: at most one parent (several requirements side by side are constraints: <T :: [A, B]>), only interfaces, no cycles (LYR-SEM0078), and no redeclaring a chain member (LYR-SEM0079) — an inherited member keeps its declaring interface, so the same call cannot dispatch two ways. What a chain does NOT add: a child interface value does not convert to the parent's type — conformance is implied for the implementing type; take the concrete value through the parent directly. std.core does not adopt Hashable :: [Equatable] yet: changing what every conforming type must implement is a breaking cut reserved for 2.0.

• Compound assignment reaches through the operator interfaces: v += w on a type conforming to Add<T> now compiles for variable targets (locals, captured variables) instead of reporting LYR-SEM0003. Field and element targets stay written out — the desugaring would evaluate the object or the index twice, and that stays visible in source.

• Block lambdas infer their return type: (x: int) => { return x * 2; } needs neither an annotation nor a context anymore — the type comes from the body's return statements, unified like match arms (return null; widens to the optional). This also closes the open-generic case: apply(5, (n) => { … }) binds U from the block. A non-void inferred lambda still needs return coverage, and disagreeing returns are one error at the lambda.

Changed

• LYR-PAR0039 retired: interface B :: [A] parses since this release; everything the parent list may not be is a semantic message now, not a parse error.

• newStringBuilder warns as deprecated — the piece v1.12 had to leave out. std.core imports nothing anymore: its extensions use private duplicates of six string natives (fromInt through charAt; the registry binds both names to the same host function), which makes std.core the library's root — and import std.core { Deprecated } inside std.string legal. Public API is unchanged; existing bytecode keeps running.

Fixed

• @Deprecated keeps its promise: it emits no metadata row and roots nothing. Previously a non-generic deprecated function survived dead-code pruning in every importing program — dead code carried along exactly because it was marked for removal.

The full changelog →