Welcome to the CMUCL Trac

CMUCL is a free implementation of the Common Lisp programming language which runs on most major Unix platforms. It mainly conforms to the ANSI Common Lisp standard. Here is a summary of its main features:

  • support for static arrays that are never moved by GC but are properly removed when no longer referenced.
  • Unicode support, including many of the most common external formats such as UTF-8 and support for handling Unix, DOS, and Mac end-of-line schemes.
  • native double-double floats including complex double-double floats and specialized arrays for double-double floats and and complex double-double floats that give approximately 106 bits (32 digits) of precision.
  • a sophisticated native-code compiler which is capable of powerful type inferences, and generates code competitive in speed with C compilers.
  • generational garbage collection on all supported architectures.
  • multiprocessing capability on the x86 ports.
  • a foreign function interface which allows interfacing with C code and system libraries, including shared libraries on most platforms, and direct access to Unix system calls.
  • support for interprocess communication and remote procedure calls.
  • an implementation of CLOS, the Common Lisp Object System, which includes multimethods and a metaobject protocol.
  • a graphical source-level debugger using a Motif interface, and a code profiler.
  • an interface to the X11 Window System (CLX), and a sophisticated graphical widget library (Garnet).
  • programmer-extensible input and output streams (Gray streams and simple-streams).
  • an Emacs-like editor, Hemlock, implemented in Common Lisp.
  • freely redistributable: free, with full source code (most of which is in the public domain) and no strings attached (and no warranty). Like the GNU/Linux and *BSD operating systems, CMUCL is maintained and improved by a team of volunteers collaborating over the Internet.

Latest News

Snapshot 2014-12

The 2014-12 snapshot has been released. See the release notes for details, but here is a quick summary of the changes between this snapshot and the previous snapshot.

  • Executables on x86 work again. They were accidentally broken when we removed support for x86.
  • PPC now supports executables. Currently executables can be made, and run, but they are rather buggy.
  • Many fixes the the LOG function, including more accurate log2 and log10 values.
    • (log (expt 2 n) 2) = n whenever (expt 2 n) would be a valid double-float number.
    • (log (expt 10 n) 10) = n whenever (expt 10 n) would be a valid double-float number.
  • Along with the iterators above, LOOP includes extensions like
    • (loop for cp being the codepoint of string ...)
    • (loop for g-string being the glyph of string ...)

Snapshot 2014-11

The 2014-11 snapshot has been released. See the release notes for details, but here is a quick summary of the changes between this snapshot and the previous snapshot.

  • ASDF 3.1.4.
  • Fixed issue where TIME returned negative cycles on ppc.
  • :UTF is no longer an alias for :UTF-8 for external formats.
  • Motifd works as a 64-bit binary (thanks to Richard Kreuter)
  • NetBSD updated to support 64-bit time_t and related values (from Robert Swindells).

A cross-compile on Darwin/x86 is needed for this release. (To get an updated and corrected EXTERN-ALIEN-NAME.)

CMUCL 20f released

CMUCL 20f has been released, For information on the changes between 20f and 20e, we refer the reader to the 20f release notes.

Because of the release, there will not be a 2014-10 snapshot.

You can find some OldNewsPost20e, OldNewsPost20d, OldNewsPost20c, OldNewsPost20b and some much older news.

Additional Information

The official web presence is at with mirrors at and at There may be some duplication between the wiki and the web pages; the wiki tends to be more up-to-date.

Other news can be found here. Or you can look here to find out where to download binaries such as the 20d binaries or a snapshot.

For a complete list of local wiki pages, see TitleIndex.

Last modified 2 months ago Last modified on 12/05/14 04:54:13