A small systems language with a regular prefix-arity grammar, single-owner memory with a default-on static borrow checker, deterministic compilation, and LLVM-based codegen.
Project site: https://nurl-lang.org · Live playground & MCP endpoint: https://play.nurl-lang.org
NURL takes a few design positions that are uncommon together:
--no-borrowck to disable) that catches use-after-move, alias-double-free, escaping closure-captures, and iterator invalidation as hard errors.| Metric | Python | C | NURL |
|---|---|---|---|
| Grammar productions | ~100 | ~200 | ~50 |
| Runtime performance | slow | fast | fast (LLVM) |
| Target platforms | one | many | any LLVM target |
A reproducible micro-benchmark suite lives in bench/ — bench/run.sh compiles and runs one source file per language N times and prints a median-ms table. Captured numbers (compute and HTTP-server peer benchmarks) are in bench/RESULTS.md and bench/HTTP_RESULTS.md; they are machine-specific, so run the suite locally for figures you can trust.
NURL source (.nu)
│
▼
Tokenizer (deterministic, context-free)
│
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Parser (LL(k≤4), ≤4-token lookahead)
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LLVM IR (.ll)
│
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clang
│
┌────┴────────────┐
▼ ▼
native wasm32-wasi
(Linux/Win/macOS) (via WASI SDK)
The compiler (compiler/nurlc.nu) is written in NURL itself. The bootstrap runs it twice over its own source and requires byte-identical LLVM IR on both rounds before the build is accepted. Details: docs/BUILDING.md.
git clone https://github.com/nurl-lang/nurl.git
cd nurl
clang -c stdlib/runtime.c -o stdlib/runtime.o # once (already checked in)
./build.sh # bootstrap + test suite
./nurl.sh examples/fizzbuzz.nu && ./fizzbuzz # compile & run a program
The only build-time dependency is clang / LLVM 14+. ./install.sh also sets up the editor extension and language server in one step. Full instructions — prerequisites per OS, manual bootstrap, DWARF debugging — are in docs/BUILDING.md; editor/LSP/formatter setup is in docs/TOOLING.md.
NURL uses prefix notation — the structure is always OP ARG1 ARG2 … ARGN. Types are single letters (i int64, u byte/uint8, f float64, b bool, s string, v void, *T pointer; sized variants i8/i16/i32, u16/u32/u64, f32); operators are sigils (: bind, = assign, @ define, → arrow, . member, ? ternary/option, ?? match, ~ loop/mutability, ! not/Result, \ closure/try, ^ return, # cast, % trait, $ import).
: | Json { JNull JBool b JNum i JStr s }
@ describe Json v → s {
^ ?? v {
JNull → `null`
JBool x → ? x `true` `false`
JNum n → ( nurl_str_int n )
JStr s → s
}
}
Calls always need parens — ( fn args ) is the only call form; a bare identifier is a name lookup. The authoritative grammar is spec/grammar.ebnf and the **normative language reference** (lexical structure, types, statements, expressions, casts) is docs/spec.md.
Single-owner memory with compiler-inserted auto-drop at scope exit — no GC, no hidden boxing. Bindings are immutable by default (: i x 0; opt into mutation with : ~). A static borrow checker — on by default, --no-borrowck to disable, --strict-borrowck to tighten — catches use-after-move, alias-double-free, escaping closure-captures, and iterator invalidation as hard compile errors, without ever changing generated code. Full model and the not-yet-checked list: docs/MEMORY.md.
The type system is strong, static, inferred, algebraic (sum types |, product types via structs), with no subtyping and no implicit conversions.
| Topic | Document |
|---|---|
| Language reference (normative) | docs/spec.md |
| Grammar (authoritative) | spec/grammar.ebnf |
| Building, bootstrap & debugging | docs/BUILDING.md |
| Tooling — editor / LSP / formatter / package manager | docs/TOOLING.md |
Canonical source format (nurlfmt) | docs/FORMAT.md |
| Memory model & borrow checker | docs/MEMORY.md |
| Async runtime (fibers) design | docs/ASYNC.md |
| Networking & MQTT client | docs/NETWORKING.md |
| Distributed stack (NAT traversal, overlay, SWIM, CRDTs) | docs/DISTRIBUTED.md |
| HTTP API, playground & MCP server | docs/PLAYGROUND.md |
| Target platforms | docs/PLATFORMS.md |
| Known limitations | docs/LIMITATIONS.md |
| Gotchas (compiler-diagnosed) | docs/GOTCHAS.md |
| Examples catalogue | examples/README.md |
| Roadmap · Changelog · Contributing | ROADMAP.md · CHANGELOG.md · CONTRIBUTING.md |
Why this matters for LLMs: the regular grammar makes generation reliable and errors local, a whole program fits in a context window, and diffs stay small. The concrete vehicle is the public MCP server at https://play.nurl-lang.org/mcp — see docs/PLAYGROUND.md.
nurl/
├── spec/grammar.ebnf — authoritative grammar (versioned snapshots alongside)
├── compiler/
│ ├── nurlc.nu — self-hosting compiler, written in NURL
│ ├── nurlc_lastgood.{nu,ll} — committed bootstrap snapshot (source + IR)
│ └── tests/ — .nu test programs + snapshot runner + golden baseline
├── stdlib/
│ ├── runtime.c — C runtime (I/O, string helpers, FFI surface)
│ ├── core/ std/ ext/ — the NURL standard library
│ └── runtime{.o,.wasm.o} — native and wasm32-wasi runtime builds
├── examples/ — curated .nu programs (see examples/README.md)
├── nurlapi/ — NURL-native container: compiler-as-a-service + playground + MCP
├── tooling/vscode-nurl/ — editor extension (syntax + LSP client)
├── tools/ — nurl-lsp, nurlfmt, nurlpkg build scripts
├── docs/ — topic documentation (see the table above)
├── bench/ — reproducible benchmark suite
├── build.sh / build.bat — full bootstrap + test-suite driver
└── nurl.sh / nurl.bat — compile a .nu file
NURL = Neural Unified Representation Language. File extension: .nu.
Copyright (c) 2026 The NURL Project Developers. Dual-licensed under either of MIT or Apache-2.0 at your option. SPDX identifier: MIT OR Apache-2.0.
Unless you explicitly state otherwise, any contribution intentionally submitted for inclusion in the work by you, as defined in the Apache-2.0 license, shall be dual-licensed as above, without any additional terms or conditions.