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A partial implementation of Clojure, in pure Ruby
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A partial implementation of Clojure in pure Ruby.

Warning: this software is alpha quality and bugridden. At this stage, Hammock is a proof of concept, and not meant to be used in production.

If there is sufficient interest, I will probably want to rewrite most of what is here, using a more disciplined approach.


Not for speed, that's for sure.

Originally, I started this project to make a version of Clojure that was fast enough to use a scripting language. As more and more of the clojure.core namespace was implemented, though, it became clear that a fast bootstrap was not going to happen using pure Ruby.

I've continued to implement much of clojure.core, though, to see how far I could take the project. It turns out, you can get pretty far. The experience has certainly leveled me up in Ruby, but I've learned a ton about Clojure's internals. In fact, even if no one ever uses this library, I will still consider it a success. If you've never implemented a Lisp before, I highly recommend it. And Ruby's flexibility lends itself to exploring this kind of thing.

Performance struggles here, adding significant weight to an already interpreted host language. That said, most "basic" Clojure programs should work as expected. The biggest performance issue stems from the limitation of "compiling" macros in an interpreted language. Nested macros compound this issue.


gem install hammock-ruby


$ hammock path/to/file.clj


$ hammock --repl


  • Persistent immutable data structures (leveraging hamster)
    • List
    • Vector
    • Map
    • Set
  • Metadata
  • Multimethods
  • Lazy sequences
  • Transducers
  • Ruby iterop
  • Multiple-arity functions
  • Macros
  • Atomic reference types (Var and Atom)
  • watches (for Atoms)
  • function composition, paritialling
  • functions for regular expressions
  • Ruby Array/Hash interop via aset, aget, etc
  • Namespaces, and require/refer
  • destructuring binding forms
  • Chunked sequences
  • try/catch/finally using Ruby exceptions

Planned Features

  • Transients
  • Protocols, and reify
  • tag-literals (data readers)
  • defrecord
  • Better printing support (via protocols)
  • sorted collections
  • read, print (the functions themselves)
  • peek/pop
  • List comprehension (via for)
  • Queue
  • promise/deliver
  • multimethod "prefer"
  • letfn (maybe?)
  • spit/slurp
  • Better error handling

Probably never, or not applicable in Ruby

  • defstruct
  • import
  • agents, refs, STM
  • thread, future, pmap (because of Ruby's GIL)
  • deftype and friends (definterface, proxy, genclass)
  • Inlinable functions
  • Type hints
  • unchecked math
  • monitors/locking
  • annotations


This project is not endorsed by Rich Hickey, but this project contains code based on his work. Such code is licensed under the following license

Copyright (c) Rich Hickey. All rights reserved.
The use and distribution terms for this software are covered by the
Eclipse Public License 1.0 (
which can be found in the file epl-v10.html at the root of this distribution.
By using this software in any fashion, you are agreeing to be bound by
the terms of this license.
You must not remove this notice, or any other, from this software.

The rest of this code also resides under the Eclipse Public License 1.0 (same as Clojure).

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