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Cloture: Clojure in Common Lisp

Cloture is an implementation of Clojure in Common Lisp. It is designed above all to interoperate well with Common Lisp; Clojure is read by the Lisp reader and Clojure namespaces are Lisp packages.

Cloture is in very early (pre-alpha) stages, but it has progressed far enough to load clojure.test, allowing the test suite to actually be written in Clojure.

Work so far has been focused on the critical path to get real Clojure code working in CL. But if there is interest from Clojurists I may work toward making it a more complete Clojure implementation.

Clojure vs. ClojureScript

Cloture is closer to Clojure than to ClojureScript. Among other things, the plan is to support Clojure’s concurrency primitives (atom, ref, agent, future, promise). However, Cloture follows ClojureScript in making exclusive use of protocols – interfaces are not used or supported. Protocol names are also derived from ClojureScript.

A note about FSet

Cloture uses FSet seqs, maps, and sets to implement Clojure vectors, maps, and sets, respectively. This involves a few hacks to FSet that might possibly affect other programs using FSet.

Starting a REPL

Use (cloture:repl) to start a Clojure REPL. You can exit the REPL with (quit) or (exit).

Note that not much work has been done yet on Clojure-style printing, so the “Print” in REPL is still mostly the Common Lisp printer.

Interoperation

Using Clojure from Lisp

The design goal of Cloture is to keep things as close to Common Lisp as possible: Clojure is read by the Lisp reader and Clojure namespaces are just packages. Clojure packages and functions, however, usually have lower-case names, so to call them from Lisp you will need to quote them with pipe characters:

(|clojure.core|:|cons| 1 '(2))
=> '(1 2)

Lisp’s nil is used only as the empty list; Clojure nil, true, and false are singletons. To use Clojure predicates from Lisp, you can use cloture:truthy? to translate.

(cloture:truthy (|clojure.core|:|=| '(1 2 3) #(1 2 3)))
=> T

Clojure files can be integrated into Lisp systems by making the system definition depend on Cloture (:defsystem-depends-on ("cloture") and using "cloture:cljc" as the file type.

(defsystem ...
  :defsystem-depends-on ("cloture")
  :components ((:file "cloture:cljc" "my-clojure-code")))

You can also use "cloture:clj" or "cloture:cljs" to load straight Clojure or ClojureScript files. Using .cljc is recommended, however.

Using Lisp from Clojure

Since Clojure uses the Lisp reader, you can call Lisp functions just by uppercasing them.

(letfn [(fst [xs] (CL:FIRST xs))]
  (fst '(1 2 3)))

You will also need to spell out CL:QUOTE and CL:FUNCTION (or refer them), as Clojure quote is not the same thing as CL quote and sharp-quote is used in Clojure for a different purpose.

(ns ...
  (:require [CL :refer [QUOTE FUNCTION]]))

All Lisp sequences (lists, vectors, and extensible sequences on implementations that support them) implement ISeq.

Reader conditionals

In reader conditionals in .cljc files (and at the REPL), Cloture looks for a :cl key.

License

Eclipse Public License.

Why?

I would like to be able to use Clojure libraries from Common Lisp.

Why “Cloture”?

Beside the obvious: cloture is a parliamentary procedure to end debate on a subject, and I would like to end certain debates. Yes, Common Lisp is “modern.” Yes, Clojure is a Lisp.

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