Racer is a knowledge representation system that implements a highly optimized tableau calculus for the description logic SHIQ(D).

Racer is the successor of the previous RacerPro system. For those of you who used the previous web site it is important to note that Racer is now freely available.

Racer provides implementations of standard reasoning problems for T-boxes and A-boxes. In addition, some non-standard inference services are provided, such as, e.g., logical abduction. Racer also provides the powerful and semantically well-defined conjunctive query language nRQL (new Racer Query Language, to be pronounced as niracle and heard as miracle), which also supports negation as failure, numeric constraints w.r.t. attribute values of different individuals, substring properties between string attributes, etc. It has convenient APIs for accessing its reasoning services from within Common Lisp and Java.

It is recommended to install the free application Portacle as a host environment. See https://portacle.github.io for downloading the Portacle application (and on MacOS do not forget the command

sudo xattr -dr com.apple.quarantine /Applications/portacle).

It is recommended to add the statements

(setq mac-option-modifier 'meta)
(setq mac-command-modifier 'super)
(setq inferior-lisp-program "lisp -\/-dynamic-space-size 20000")
(setq confirm-kill-emacs nil)
(setq default-directory "~/")

to the Portacle init file /Applications/portacle/config/user.el. With the first form, the meta key is set properly as the option key (e.g., for MacOS), with the second form the lisp system gets more memory. With the third form Emacs does not ask when quitting, and with the last form the default directory for opening files is selected. One might also consider adding

(ql:quickload "racer")
(in-package :racer-user)

to the Portacle SBCL init file /Applications/portacle/config/site-init.lisp. Then, just starting the Portacle application in the finder puts Racer into operation. After the installation is completed, Racer is ready to use by double-clicking the Portacle application.

Give the focus is on the uppoer Emacs windwo, just choosing Compile/Load File from the menu or pressing c-c-c-k evaluates the forms in the above window and prints query results into the REPL as shown in the figure.

An open source version of Racer is also available at Github.com. Racer can easily be installed via Quicklisp (http://quicklisp.org) with (ql:quickload "racer"). Note that Racer requires ASDF 2.32. This is relevant for Lispworks, for which also (setf asdf::*default-encoding* :default) should be evaluated.

Racer is distributed under the following BSD 3-clause license.