Goop

OCaml-style safety on Go’s runtime.

• Exhaustive ADTs and pattern matching
• Branded IDs (single-ctor ADTs) so order_id ≠ symbol
• Go interop and deploy — same runtime, stdlib, and binaries
• Cache-only builds — edit .goop, run goop build / goop test

Non-exhaustive match (EXHAUST003)

type OrderAck =
  | Filled of { order_id: string; qty: int }
  | Rejected of { reason: string }
  | PartialFill of { order_id: string; filled: int; remaining: int }

let handleAck (ack: OrderAck) : string =
  match ack with
  | Filled { order_id; qty } -> order_id
  | Rejected { reason } -> reason
  (* forgot PartialFill — Go compiles; Goop does not *)

✕ EXHAUST003: non-exhaustive match: missing constructor(s): PartialFill

Getting started

cd src && go build -o ../goop ./cmd/goop
../goop check docs/examples/hello.goop
../goop build docs/examples/hello.goop   # → ./goop-out (Go stays in $GOOP_HOME/build)
./goop-out
../goop test tests/

Generated .go never lands in your project tree by default. See CLI artifacts · tutorial.

How Goop compares

Compile-time checks that Go leaves to tests, panics, or -race. Style: STYLE.md.

Safety feature	Go	Rust	OCaml	Goop
Sum types + exhaustive match	❌	✅	✅	✅
No null by default (option)	❌	✅	✅	✅
Branded IDs (single-ctor ADT)	❌	✅	✅	✅
Effect handlers (OCaml 5-style)	❌	❌	✅	✅ (CPS-lowered)
Nil channel misuse	❌ (runtime)	N/A	N/A	✅ (NIL001)
Data race detection	⚠️ -race	✅	❌	✅ (linear, conservative)
Refinement / contracts	❌	⚠️	⚠️	✅ VC + optional Z3
Native Go stdlib + deploy	✅	❌	❌	✅

Go interop

Call Go packages, implement Go interfaces in Goop, and embed Go when needed:

module main

import go "strings" {
  val ToUpper : string -> string
}

@[go] {
  func greet(name string) string {
    return "Hello, " + name + "!"
  }
}
val greet : string -> string

let main () : unit =
  print_line (greet (ToUpper "goop"))

import go / import goop · implements · Go methods/fields · @[go] / @[c] embeds. Examples: extern_demo.goop · go_method_calls.goop · go_implements_slog_handler.goop.

Language & status

Everyday surface: STYLE.md · docs/examples/.

Current: v1.8.0 — cache-only goop build / compile under $GOOP_HOME/build, with transitive import goop deps. Prior highlights: Go struct/slog FFI (1.7), cross-package libraries (1.6), call lowering (1.5). Full history: CHANGELOG · RELEASE_NOTES.

FAQ

Production-ready? The compiler, checker, codegen, LSP, and e2e suite ship and are exercised in CI. Some OCaml corners are pragmatic subsets; we are not claiming production load readiness yet.

Borgo / Dingo? Goop is a full compiler with OCaml-aligned syntax and compile-time safety for gradual Go migration. Dingo-style ? and F# computation expressions were removed in 1.0.

Need OCaml or Z3? No. Pattern matching from Rust/Swift/Kotlin transfers. Z3 is optional ([check] smt = true).

Documentation

Resource	Link
Tutorial	Getting started through concurrency
Stdlib	Prelude, builtins, std.*
Design	STYLE, CLI artifacts, FFI
Examples	Runnable; CI goop check
Contributing	Build and test workflow

License

MIT / Apache-2.0 dual license.