Jolt

A Clojure implementation on Chez Scheme. Jolt reads Clojure source, analyzes it to a host-neutral IR, emits Scheme, and runs it on Chez. The compiler is self-hosted: it is written in Clojure (jolt-core/) and compiles itself. It ships a Clojure-compatible standard library.

Requirements

Only Chez Scheme (the gate invokes it as chez). The conformance gate additionally uses Clojure on the JVM as an oracle, but running jolt does not.

Build

There is no build step. The bootstrap seed (host/chez/seed/{prelude,image}.ss) is checked in, so a fresh clone runs immediately:

git clone --recurse-submodules https://github.com/jolt-lang/jolt.git
cd jolt
bin/joltc -e '(+ 1 2)'        # => 3

After changing a compiler source — the reader (host/chez/reader.ss), the analyzer/IR/backend (jolt-core/jolt/*.clj), or the clojure.core overlay (jolt-core/clojure/core/*.clj) — re-mint the seed:

make remint                   # iterates host/chez/bootstrap.ss to a byte-fixpoint

Run

bin/joltc -e EXPR             # evaluate a Clojure expression and print the result

$ bin/joltc -e '(->> (range 10) (filter even?) (map (fn [x] (* x x))) (reduce +))'
120
$ bin/joltc -e '(/ 1 2)'
1/2

Compile a binary

bin/joltc build ahead-of-time compiles a project into a single self-contained executable — the runtime, clojure.core, the standard library, the app, and its deps.edn dependencies are linked in, so the result needs no Chez install, no JVM, and no source on disk to run.

bin/joltc build -m myapp.core -o myapp   # compile myapp.core's -main into ./myapp
./myapp arg1 arg2                        # runs anywhere; args reach -main

Modes trade dynamism for speed: the default (release) build uses the proven code generator; --opt also runs the inference + inlining + scalar-replacement passes over the closed-world program; --dev is unoptimized.

Two opt-in closed-world flags cut dispatch cost and binary size:

bin/joltc build -m myapp.core --direct-link   # app->app calls bind directly (no var lookup)
bin/joltc build -m myapp.core --tree-shake    # ship only code reachable from -main

--tree-shake walks the call graph across your app, its libraries, and clojure.core, drops everything unreachable from -main (and the compiler itself when the app never evals), and typically removes 1–2 MB. It stays sound by bailing out — keeping everything, and reporting which library is responsible — when reachable code resolves vars by name at runtime (eval/resolve/ns-resolve/…). See docs/tools-deps.md and docs/rfc/0007.

This needs Chez's kernel development files (libkernel.a, scheme.h) and a C compiler. They come with a from-source Chez install; a distro chezscheme package ships only the runtime, so build won't link a binary there. RFC 0007 (docs/rfc/) covers the design and the three-mode model.

Architecture

A small Chez runtime (host/chez/*.ss: value model, persistent collections, seqs, vars/namespaces, host interop) hosts a portable Clojure overlay split across two source roots by when they load:

• jolt-core/ is baked into the seed — the compiler (jolt-core/jolt/: reader/analyzer/IR/backend, plus jolt.main/jolt.deps) and clojure.core in dependency-ordered tiers (jolt-core/clojure/core/NN-*.clj). Changing anything here means re-minting the seed.
• stdlib/ loads lazily at runtime off the source roots — the rest of the standard library (clojure.string/set/walk/edn/pprint/…) plus the jolt.ffi host library. Editing these needs no re-mint.

bin/joltc loads the checked-in seed and the spine, then compiles and evaluates on Chez (read → analyze → IR → emit → eval). host/chez/bootstrap.ss rebuilds that seed from source on pure Chez; the build is a self-hosting fixpoint (a rebuild reproduces the checked-in seed byte-for-byte).

Differences from Clojure

Jolt targets Clojure semantics but runs on Chez, not the JVM. Most portable Clojure runs unchanged — persistent collections (32-way-trie vectors, HAMT maps/sets), the numeric tower (exact integers, bignums, ratios, doubles), lazy and infinite sequences, transducers, destructuring, multimethods with hierarchies, protocols/records (deftype/defrecord/reify/extend-protocol), metadata, namespaces, atoms, future/promise/agent/pmap, clojure.core.async, runtime eval/load-string/defmacro, and the full reader (#(), #_, #?, tagged literals, #"…") all behave as on the JVM. = is category-aware ((= 3 3.0) ⇒ false) and == is value-equality, as in Clojure. The genuine divergences:

• No JVM, no Java interop. No reflection, no gen-class/proxy. Interop syntax (Class., Class/static, .method) resolves only against a shimmed subset of the java.* standard library; a class token is a name, not a loaded class. See docs/host-interop.md. To call C libraries directly, use the jolt.ffi foreign-function interface (how the db and http-client libraries bind SQLite/libpq and sockets/OpenSSL/zlib).
• No BigDecimal. decimal? is always false and there is no M literal; the rest of the numeric tower matches the JVM.
• No STM. No ref/dosync/alter/commute — coordinated shared state uses atoms (per-atom mutex, JVM-style CAS). The concurrency primitives above are otherwise present and run on a shared heap.
• Regex engine. Patterns compile through irregex (vendored), not java.util.regex; common patterns work, Java-specific features can differ.
• Coverage. clojure.core is implemented function by function against the JVM-sourced conformance corpus — broad but not total; a namespace can load with most functions working and a few not yet implemented.

Test

make test                     # the full gate
make corpus                   # conformance corpus vs the JVM-sourced spec
make unit                     # host-specific unit cases
make selfhost                 # bootstrap fixpoint (rebuild == checked-in seed)
make smoke                    # bin/joltc CLI smoke
make sci                      # load borkdude/sci's source through joltc (compat stress)
make ffi                      # HTTP-server GC-safety + http-client temp paths
make transient                # transient mutation + linear-time builds
make certify                  # JVM oracle (skips if clojure is absent)

The conformance corpus (test/chez/corpus.edn) is a host-neutral language spec whose expected values are sourced from reference JVM Clojure. See test/conformance/SPEC.md.

License

Eclipse Public License 2.0