Feature Status

By Christian Findlay 08 Sep 2026

Osprey is an alpha language. The compiler is written in Rust, emits LLVM IR and builds native executables, wasm32-wasip1 modules, and app-logic libraries for iOS and Android. Each target has an explicit runtime boundary.

Current version: v0.16.0.

Releases

Implemented foundations

• Default (.osp) and ML (.ospml) source parsing, both lowering to the same AST before semantic analysis
• Hindley–Milner type inference, algebraic data types and exhaustive pattern matching for supported patterns
• Typed effect operations, lexical handlers, compile-time rejection of missing handlers, and single-shot resume for --target=native
• Immutable persistent lists and maps
• Lightweight native fibers and channels
• Native HTTP, WebSocket, file, process and C FFI runtime APIs
• Default, tracing-GC and Perceus-ARC native memory backends
• Native and wasm32-wasip1 compilation, plus iOS and Android C ABI targets
• A shared modular mobile application with reactive native UI, SQLite cache, live GitHub requests, and local notes and priorities
• Compiler-backed formatting, documentation generation, testing, profiling and language-server commands

The runnable programs in tests/regressions/ are compiled and compared with checked-in expected output.

Target support

The compiler rejects unsupported target operations during --check, --llvm, and compilation. iOS and Android reject resume and unavailable built-in process, HTTP, and WebSocket operations. Their hosts provide platform networking through the C boundary. WebAssembly also rejects fibers, terminal control, and arbitrary C imports; approved browser imports and supported host filesystem operations remain available.

Issue Inbox demonstrates the same Osprey project on iOS and Android, including ML modules and a small Default-flavor C entry point. Its screenshots come from actual simulator/emulator runs. The iOS app has also been installed and verified on a physical iPhone. Both Android ABIs execute the shared test corpus through the C ABI.

Current limits

• Resumable effects are supported by --target=native. Mobile C ABI targets and WebAssembly reject them at compile time; supported handlers that return immediately remain usable.
• The effect checker follows operations through the closed program, including exported mobile functions. It does not yet provide general polymorphic effect-row variables in public higher-order signatures.
• Tail-call optimisation is not implemented.
• User-defined generics and the package manager remain roadmap work. Working project/module examples do not imply every module-system feature is complete.
• The strict static-memory mode described in the memory specification is not a current CLI option. Native builds accept default, gc, and arc; mobile and WebAssembly accept default only.
• The initial mobile runtime retains general allocations for process lifetime and has no public library teardown or returned-string release API.
• The mobile sample reads one public GitHub issue page. Authentication, pagination, background refresh, and posting changes to GitHub are not implemented.
• C integrations are outside Osprey's memory-safety guarantee.

For detailed intended behavior and chapter-specific implementation notes, read the specifications. For compiler-generated built-in signatures, use the API reference.