Introduction

Osprey is a statically-typed functional language in the ML family. It compiles to native code via LLVM.

Core Features

• Hindley-Milner type inference; explicit annotations are optional.
• Pattern matching as the only conditional construct (no if/else).
• Immutable bindings by default; mut opts in to mutability.
• Algebraic effects checked at compile time.
• Result<T, E> for all fallible operations; no exceptions, panics, or null.
• Named arguments required for functions of two or more parameters.
• Lightweight fibers and channel-based concurrency.
• Automatic memory management with no observable collector — ARC by default, tracing GC selectable, and a --static-memory mode with zero runtime memory operations.
• Built-in HTTP and WebSocket support.

Status

This specification is the authoritative source for Osprey syntax and behaviour. The language and compiler are under active development; implementation status is called out per chapter where it diverges from the specification.