A small ML-family programming language with region-based memory (no GC), effects as ordinary capability values, and five backends: interpreter, C, LLVM IR, Wasm, and RV32IM. The first four are held to each other by a parity suite that compares their output byte for byte; the fifth boots under QEMU — the one implementation in the stack nobody here wrote.

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.

The policy is dogfood-first: nothing graduates out of mere/contrib/ until there is an external consumer asking for independent versioning. mere-vscode is separate because the coupling is a protocol rather than a filesystem — the extension does not read a line of the compiler's source, it starts mere lsp and speaks LSP.

• 2526 tests, cross-backend parity over 112 programs, and about thirty differential gates in CI that compare Mere against external oracles (protoc, grpcurl, graphql-js, python h2 / hpack, html5lib, QEMU, Blargg's Game Boy suite, and others).
• Self-hosting at a fixpoint: the Mere-in-Mere compiler, compiled by itself and run as Wasm, emits byte-identical output to the reference.
• A fifth backend, and an operating system on it: mere -rv emits a flat RV32IM binary with no external assembler or linker, and --bare hands the program the machine instead of a host — raw memory arrives as an unforgeable window capability and traps are ordinary closures. On that: a preemptive scheduler, a shell, a syscall boundary, and the self-hosted compiler running as a user process on a RISC-V CPU also written in Mere, emitting WAT byte-identical to the native one.
• Editor support out of the compiler's own answers: diagnostics, hover, definition, completion, outline, formatting, semantic tokens, references and rename, served by mere lsp.

• Memory model: 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.
• Borrow annotations: four modes (&R T / &mut R T / &shared write R T / &exclusive R T) covering the full 10-pair conflict matrix, checked statically.
• Backends that are held to each other: anything the interpreter runs also runs as a native binary, as LLVM IR and as Wasm, compared byte for byte — and where they legitimately differ, the difference is pinned so it keeps being asked about rather than tolerated.

curl -fsSL https://raw.githubusercontent.com/merelang/mere/main/scripts/install.sh | sh
mere examples/factorial.mere

Docs, tutorial and a Wasm playground: merelang.org.

All merelang repositories ship under the MIT license.