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Clasp — Bringing Common Lisp and C++ Together

NOTE: September 7, 2021 - This contains a pre-release of Clasp 1.0.

You need to use the release version of llvm13. Packaged version should do nicely (e.g. brew for macos)

We have a talk up on youtube


Clasp is a new Common Lisp implementation that seamlessly interoperates with C++ libraries and programs using LLVM for compilation to native code. This allows Clasp to take advantage of a vast array of preexisting libraries and programs, such as out of the scientific computing ecosystem. Embedding them in a Common Lisp environment allows you to make use of rapid prototyping, incremental development, and other capabilities that make it a powerful language.

For more information on using Clasp, see:

Latest Release

The upcoming release is Clasp 1.0. Changes


Building Clasp

At the moment, Clasp is supported on Linux, Mac OS X and FreeBSD. On these systems, you should be able to build it from source.

Follow the instructions.

In case things go wrong, the quickest way to get help is to either file an issue, or to chat with us directly.

Building takes a lot of resources. In parallel mode ('USE_PARALLEL_BUILD = True' in wscript.config) you will not be able to survive with only 8 GB of RAM and it will be 1-2 hours build time. If you have 8 GB of RAM you can turn off the parallel build which will then run for a day or so. Make sure to have some paging space ("swapfile") configured.

There is a docker image for a superset of Clasp called Cando

Currently there are no binary releases available, however you can extract a working /opt/clasp tree for Debian 10 out of the docker image.

Common Lisp Ecosystem Support

Clasp supports the following major components:

Post on the issues or contact us if you're interested in changing that.

Contributing to Clasp

We very much welcome any kind of contribution to Clasp, even if it is just bug finding and testing. A lot can be done all around the project, if you want to dive into something large. See the CONTRIBUTING file for the few guidelines we've set up around contributions.

Reporting Problems

Generally you can report problems in two fashions, either by opening an issue ticket or by chatting with us directly. In both cases, though, you should have the following pieces handy in order for us to be able to help you out as quickly and painlessly as possible:

  • Your operating system name and version.
  • The branches that you're using of Clasp and Externals-Clasp.
  • A paste of the build log or failure point that you reached.
  • Patience.


Clasp has an IRC channel on Libera called #clasp. If you have questions, problems, suggestions, or generally would like to just hang out with us devs, come and stop by!

More on Clasp

For more information on Clasp and the discussion around it, see the following sites:


Clasp was supported by:

  • The Defense Threat Reduction Agency (DOD-DTRA) (HDTRA1-09-1-0009)
  • The National Institutes of Health (NIH/NIGMS Grant number: 2R01GM067866-07A2)
  • The National Science Foundation (Grant number: 1300231)