94 lines
4.1 KiB
Markdown
94 lines
4.1 KiB
Markdown
# Jolt
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A Clojure interpreter running on [Janet](https://janet-lang.org). Jolt reads Clojure source, evaluates it with an interpreter written in pure Janet, and ships a Clojure-compatible standard library. The goal is a Janet-hosted [SCI](https://github.com/borkdude/sci) runtime — a minimal bootstrap that loads SCI's Clojure source as its standard library.
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## Build
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```bash
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git clone https://github.com/yogthos/jolt.git
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cd jolt
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git submodule update --init # pulls vendor/sci
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jpm build # compiles build/jolt
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```
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Requires Janet ≥ 1.36 and `jpm`.
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## Run
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```
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build/jolt # start a REPL
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build/jolt file.clj [args] # run a file (binds *command-line-args* and *file*)
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build/jolt -e EXPR [args] # evaluate EXPR and print the result
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build/jolt -h # help
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```
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The REPL accumulates multi-line forms until they balance:
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```
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user=> (defn fib [n] (if (< n 2) n (+ (fib (- n 1)) (fib (- n 2)))))
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#'user/fib
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user=> (map fib (range 10))
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(0 1 1 2 3 5 8 13 21 34)
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```
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Running a file evaluates its top-level forms:
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```
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$ echo '(println "hello" (* 6 7))' > hello.clj
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$ build/jolt hello.clj
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hello 42
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```
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## Use as a library
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```janet
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(use jolt/api)
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(def ctx (init))
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(eval-string ctx "(+ 1 2)") # → 3
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(eval-string ctx "(map inc [1 2 3])") # → [2 3 4]
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```
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`(init)` returns a context with `clojure.core` loaded. Each context is isolated; use separate contexts for separate environments.
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## Host interop
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Jolt exposes CLJS-style host interop through `.` on any Janet table or struct — a field holding a function is called with the receiver as the first argument:
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```clojure
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(def obj {:greet (fn [self name] (str "Hello " name))})
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(. obj greet "Alice") ; → "Hello Alice"
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(.-greet obj) ; field access (reader sugar for (. obj :greet))
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```
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Janet's standard library is reachable through `jolt.interop` (and the `jolt.shell` / `jolt.http` helpers built on it):
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```clojure
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(require '[jolt.interop :as j])
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(j/janet-type [1 2]) ; → :tuple
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(j/janet-table-keys {:a 1 :b 2}) ; → [:b :a]
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```
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## Differences from Clojure
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Jolt targets Clojure semantics but runs on Janet, not the JVM. The notable divergences:
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- **Host platform.** No JVM and no Java interop — `import`, `gen-class`, `proxy` of Java classes, and `java.*` are unavailable. `instance?` recognizes a small set of built-in types (`clojure.lang.Atom`, `Number`, `String`, …).
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- **Numbers.** Janet integers and doubles only — no bignums, ratios, or `BigDecimal`. `(/ 1 3)` is `0.3333…`, large products lose precision, and there are no auto-promoting `+'`/`*'`. `quot`/`rem`/`mod` follow Clojure's sign rules. `bigint`, `rational?`, and `class` are not provided.
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- **Collections.** Vectors are Janet tuples, lists are Janet arrays; maps and sets are persistent hash structures. Value equality and sequence operations are Clojure-compatible, but hash-map/hash-set iteration order is unspecified and differs from Clojure — use `sorted-map`/`sorted-set` when order matters.
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- **Concurrency / STM.** Single-threaded. No refs, `dosync`, agents, or `send`; `locking` evaluates its body without real locking. Atoms, volatiles, and delays are supported.
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- **Regex.** Compiled to Janet's PEG engine (Janet has no regex). Supported: capturing groups (`[whole g1 …]`), greedy and lazy quantifiers with backtracking, `(?:…)`, lookahead `(?=…)`/`(?!…)`, alternation, anchors `^ $ \b \B`, character classes, and the `(?i)` flag. Not supported: lookbehind, backreferences (`\1`), and named groups (`(?<name>…)`).
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- **Not implemented.** Transients (`transient`/`persistent!`), JVM reflection, and `proxy`. (`reify` and `extend-protocol` work for Jolt protocols.)
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Supported and Clojure-compatible: chars as a distinct type, lazy/infinite sequences, transducers, destructuring, multimethods with hierarchies, protocols/records, metadata, namespaces, and the reader (`#()`, `#_`, `#?`, tagged literals, `#"…"`).
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## Test
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```
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jpm test # full test suite
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janet test/conformance.janet # Clojure-conformance battery
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```
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## License
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[Eclipse Public License 1.0](https://opensource.org/licenses/EPL-1.0)
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