Osprey for VS Code

Preview. Osprey is pre-production and evolving fast. Expect rough edges.

Language support for Osprey — a functional programming language with algebraic effects, fiber-based concurrency, pattern matching, and strong compile-time safety.

One core. Two surfaces. Zero compromise. Osprey is one language — one Hindley-Milner type checker, one effect system, one runtime, one standard library, one LLVM/wasm backend — fronted by two first-class flavors:

• Default flavor (.osp) — the accessible surface: C-style braces, fn, f(x: a, y: b) calls with named arguments, if/else if/else. Borrows the shapes of Kotlin, Swift, Go, Dart, C#, and Java so it reads like home. Fully implemented today.
• ML flavor (.ospml) — the uncompromising surface: offside-rule layout (indentation, no braces), curry-by-default, whitespace application f a b, \x => e lambdas, := mutation. The best of the ML family, all the way — no C-isms, no concessions. In active development.

Neither flavor is the watered-down one: the surface goes all the way in your direction. Mainstream developers get a surface that reads like the languages they already know; FP devotees get real layout and real currying. Pick your tribe and go all in — nobody is forced into the other camp's spelling.

Select the flavor per file (the .ospml extension, a leading // osprey: flavor=ml marker, or the --flavor ml CLI flag — all shipping today). Because both flavors lower to the same canonical AST before any type checking, the design lets a .osp file and a .ospml file live in one folder and compile into a single program, sharing one type checker, one effect system, and one binary.

Powered by a Rust language server (osprey lsp, built on lspkit) that runs the compiler front-end in-process — the same engine targeted at Neovim and Zed next.

Features

• Syntax highlighting — keywords, types, string interpolation ("Hello ${name}!"), operators, and comments. Default (.osp) is fully supported today; ML (.ospml) support is rolling out alongside the flavor.
• Live diagnostics — errors and warnings from the Osprey compiler as you type, inline in the editor (full for Default .osp; ML .ospml diagnostics track the in-development ML front-end).
• Hover, go-to-definition, find-references, document symbols, signature help, and completion — driven by the compiler's own parser and type checker.
• Compile & run from the editor:
  • Osprey: Compile Osprey File (Ctrl/Cmd+Shift+B)
  • Osprey: Compile and Run Osprey File (F5)
• Bracket matching, auto-closing, and comment toggling.

Requirements

The extension bundles a version-matched Osprey compiler for your platform and verifies it at startup, so syntax checking works out of the box.

To compile and run programs, Osprey invokes LLVM and a C toolchain, so install:

• LLVM (provides llc) — brew install llvm / scoop install llvm
• A C compiler — clang (macOS/Linux) or MinGW gcc (scoop install gcc)

Or install the full toolchain via a package manager (this also puts osprey on your PATH):

brew install nimblesite/tap/osprey            # macOS / Linux
scoop bucket add nimblesite https://github.com/Nimblesite/scoop-bucket && scoop install osprey   # Windows

Settings

Links

• Website & docs: https://ospreylang.dev
• Source & issues: https://github.com/Nimblesite/osprey

License

See LICENSE.