Finding Lisp Libraries

While the standard library of functions, data types, and macros that comes with Common Lisp is quite large, it provides only general-purpose programming constructs. Specialized tasks such as writing GUIs, talking to databases, and parsing XML require libraries beyond what are provided by the ANSI standardized language.

The easiest way to obtain a library to do something you need may be simply to check out your Lisp implementation. Most implementations provide at least some facilities not specified in the language standard. The commercial Common Lisp vendors tend to work especially hard at providing additional libraries for their implementation in order to justify their prices. Franz’s Allegro Common Lisp, Enterprise Edition, for instance, comes with libraries for parsing XML, speaking SOAP, generating HTML, connecting to relational databases, and building graphical interfaces in various ways, among others. LispWorks, another prominent commercial Lisp, provides several similar libraries, including a well-regarded portable GUI toolkit, CAPI, which can be used to develop GUI applications that will run on any operating system LispWorks runs on.

The free and open-source Common Lisp implementations typically don’t include quite so many bundled libraries, relying instead on portable free and open-source libraries. But even those implementations usually fill in some of the more important areas not addressed by the language standard such as networking and multithreading.

The only disadvantage of using implementation-specific libraries is that they tie you to the implementation that provides them. If you’re delivering end-user apps or are deploying a server-based application on a server that you control, that may not matter a lot. But if you want to write code to share with other Lispers or if you simply don’t want to be tied to a particular implementation, it’s a little more annoying.

For portable libraries—portable either because they’re written entirely in standard Common Lisp or because they contain appropriate read-time conditionalization to work on multiple implementations1--your best bet is to go to the Web. With the usual caveats about URLs going stale as soon as they’re printed on paper, these are three of the best current starting points:

• Common-Lisp.net (http://www.common-lisp.net/) is a site that hosts free and open-source Common Lisp projects, providing version control, mailing lists, and Web hosting of project pages. In the first year and a half after the site went live, nearly a hundred projects were registered.
• The Common Lisp Open Code Collection (CLOCC) (http://clocc.sourceforge.net/) is a slightly older collection of free software libraries, which are intended to be portable between Common Lisp implementations and self-contained, not relying on any libraries not included in CLOCC itself.
• Cliki (http://www.cliki.net/) is a wiki devoted to free software in Common Lisp. While, like any wiki, it may change at any time, typically it has quite a few links to libraries as well to various open-source Common Lisp implementations. The eponymous software it runs on is also written in Common Lisp.

Linux users running the Debian or Gentoo distributions can also easily install an ever-growing number of Lisp libraries that have been packaged with those distributions’ packing tools, apt-get on Debian and emerge on Gentoo.

I won’t recommend any specific libraries here since the library situation is changing every day—after years of envying the library collections of Perl, Python, and Java, Common Lispers have, in the past couple of years, begun to take up the challenge of giving Common Lisp the set of libraries—both open source and commercial—that it deserves.

One area where there has been a lot of activity recently is on the GUI front. Unlike Java and C# but like Perl, Python, and C, there’s no single way to develop GUIs in Common Lisp. Instead, it depends both on what Common Lisp implementation you’re using and what operating system or systems you want to support.

The commercial Common Lisp implementations usually provide some way to build GUIs for the platforms they run on. Additionally, LispWorks provides CAPI, the previously mentioned, portable GUI API.

On the open-source side, you have a number of options. On Unix, you can write low-level X Windows GUIs using CLX, a pure-Common Lisp implementation of the X Windows protocol, roughly akin to xlib in C. Or you can use various bindings to higher-level APIs and toolkits such as GTK and Tk, much the way you might in Perl or Python.

Or, if you’re looking for something completely different, you can check out Common Lisp Interface Manager (CLIM). A descendant of the Symbolics Lisp Machines GUI framework, CLIM is powerful but complex. Although many commercial Common Lisp implementations actually support it, it doesn’t seem to have seen a lot of use. But in the past couple years, an open-source implementation of CLIM, McCLIM—now hosted at Common-Lisp.net—has been picking up steam lately, so we may be on the verge of a CLIM renaissance.