Status

nova-nix evaluates real nixpkgs. import <nixpkgs> {} resolves the top-level package set (~23,000 attributes) to weak head normal form, and a package evaluates through the stdenv bootstrap down to a derivation:

$ NIX_PATH=nixpkgs=/path/to/nixpkgs \
    nova-nix eval --expr '(import <nixpkgs> { system = "x86_64-linux"; }).hello.drvPath'
"/nix/store/gciipqhqkdlqqn803zd4a389v86ran45-hello-2.12.1.drv"

That drvPath, and the 253-derivation closure behind it, byte-matches upstream nix-instantiate — verified in CI on the same nixpkgs tree. It targets the Nix 2.24 language. Evaluation and derivation-hash parity are done; building on Windows is the work ahead.

Quickstart

git clone https://github.com/Novavero-AI/nova-nix.git
cd nova-nix
cabal build

$ nova-nix eval --expr '1 + 2'
3

$ nova-nix eval --expr 'builtins.map (x: x * x) [ 1 2 3 4 5 ]'
[ 1 4 9 16 25 ]

$ nova-nix eval FILE.nix                       # evaluate a file
$ nova-nix build FILE.nix                       # build a derivation
$ nova-nix --nix-path nixpkgs=/path eval FILE.nix

How it works

Six layers — Haskell for logic, C99 for data:

1. Parser (Nix.Parser, Nix.Expr) — hand-rolled recursive descent; the full Nix grammar to a 19-constructor AST.
2. Evaluator (Nix.Eval) — the AST compiles to a flat 24-opcode bytecode that a lazy, thunk-memoizing evaluator runs. Recursive let/rec are knot-tied; reference cycles are caught by blackhole detection. The evaluator is polymorphic over its effect via MonadEval — PureEval for tests, EvalIO for the real thing.
3. Data layer (cbits/nn_*.c) — nine arena-allocated C99 modules (interned symbols, sorted attrsets, thunks, environments, lists, context strings, bytecode, lambdas) hold evaluation data off the GHC heap. Haskell calls C to create and query it; C never calls back.
4. Store (Nix.Store) — content-addressed /nix/store (C:\nix\store on Windows) with SQLite metadata and reference scanning.
5. Builder (Nix.Builder) — dependency graph, topological sort, and binary-cache substitution before local builds.
6. Substituter (Nix.Substituter) — the HTTP binary-cache protocol: narinfo parsing, Ed25519 verification, NAR download and unpack. Built on nova-cache.

Two decisions shape the rest. Haskell owns evaluation, C owns data layout — bulk eval state lives off the GHC heap, so large evaluations don't thrash the collector. And derivation is a lazy wrapper over the eager derivationStrict primop (as in Nix's corepkgs/derivation.nix), so referencing a package never forces its build closure.

Windows-native

Roadmap

Done — parser, lazy bytecode evaluator, the Nix builtins set, the C99 data layer, content-addressed store, derivation builder, binary-cache substituter, import <nixpkgs> {} evaluation, and derivation-hash parity with upstream Nix (hello's 253-derivation closure byte-matches nix-instantiate).

Next

• Windows stdenv — MinGW GCC + MSYS2 coreutils bootstrap for native builds.
• Parity across more of nixpkgs — extend the byte-match check beyond hello's closure.
• Substituter — XZ decompression and real NAR hashing (currently uncompressed-only, with a placeholder hash).

Library usage

import Nix.Parser (parseNix)
import Nix.Eval (PureEval (..), eval)
import Nix.Builtins (builtinEnv)

main :: IO ()
main = case parseNix "<expr>" "let x = 5; in x * 2 + 1" of
  Left err   -> print err
  Right expr -> print (runPureEval (eval (builtinEnv 0 []) expr))  -- Right (VInt 11)

The evaluator is polymorphic over MonadEval: PureEval for deterministic tests, EvalIO for filesystem access.

Build & test

cabal build
cabal test

Requires GHC 9.8+ and cabal-install 3.10+.

_{BSD-3-Clause · Novavero AI}