A small ML-family programming language with explicit region-bound memory, capability-passing effects, and feature-parity codegen to interp + C + LLVM + Wasm.

The name Mere is Old English for "lake" — the region metaphor (a body bounded from its surroundings), the minimal ML-family ring, and a modest "just a …" nuance.

More repos may be split out as the language stabilises (a tree-sitter grammar and a dedicated DOM bindings library are the obvious next candidates), but the policy is dogfood-first: nothing graduates out of mere/contrib/ until there is an external consumer asking for independent versioning.

• 1580 tests across interp + C + LLVM + Wasm. 16 realistic examples (~2500 LoC; toy_sql.mere alone is 1165 LoC) match diff = 0 PERFECT across all four backends.
• Phase 48 (frontend FFI MVP) shipped 2026-06-25 — Mere code now runs interactively in the browser via DOM bindings + an exported Wasm function table that lets JavaScript dispatch back into Mere closures. See counter demo.
• mere fmt is the built-in source formatter with --check for CI / pre-commit (Phase 47).

• Memory model: 5 strategies (owned / borrowed / region / view / stack) chosen at the type level, not auto-inferred. Region values are Trivial[R] by default; with handles Drop types in LIFO scope order.
• Effects as values: capabilities are passed as ordinary function arguments — no monad-of-the-month, no effect rows. The bucket-brigade is intentional and shape-of-signature-aliased.
• Borrow annotations: four modes (&R T / &mut R T / &shared write R T / &exclusive R T) cover the full 10-pair conflict matrix, checked statically.
• 4-backend feature parity: anything in interp also runs as C native binary, LLVM IR, and Wasm — verified by diff = 0 on the same example set.

git clone git@github.com:merelang/mere
cd mere
dune build
dune exec mere -- examples/factorial.mere   # interpreter
dune exec mere -- -c examples/factorial.mere | clang -x c - -o fact && ./fact  # C
dune exec mere -- -w examples/factorial.mere > fact.wat && wat2wasm fact.wat   # Wasm

Full tutorial: docs/tutorial.md.

All merelang repositories ship under the MIT license.