Implementation status and known gaps

The language specification and implementation status are intentionally separate.

• Language Reference defines valid surface programs.
• Language Design defines core semantics.
• Implementation Plan owns current completion, phases, reference targets, and verified suite results.
• tests/conformance/catalog.json records feature-level executable expectations.

Reading guide callouts

Available means the described path has current reference implementation coverage. Partial names a supported boundary and its remaining gap. Specified means the rule is normative but execution support is planned.

A normatively valid XFAIL is not a negative language example. A parser form absent from the reference is not made portable by accidental acceptance.

Stable current boundary

LLVM native is the sole reference execution backend. Front-end checks remain authoritative for parsing, typing, elaboration, diagnostics, and invalid programs. Volatile counts and timings should be read directly from the Implementation Plan rather than copied into this guide.

Prominent remaining areas

At the time this guide edition was generated, major named gaps included explicit laziness, general target planning and fallback, non-native providers, structured concurrency, recursive lexical handler lowering, generic provider ABI coverage, and separate compiled library artifacts. Always consult the plan for the current list.

The bundled Effect library also still spells its state contract as unparameterized State with an implicit element type, while the approved effect design and the Language Reference’s handler example use State(s). This is a library/reference discrepancy, not an alternative surface-language rule.