There seems to be a bug in the LispWorks backend when it comes to getting the callers of a function. To replicate, evaluate the following in the swank package: ? (xref :callers "LIST-CALLERS") Error in LispWorks: Undefined function T in form (SYMBOL-FUNCTION T). ? (list-callers 'list-callers) Error in LispWorks: Undefined function T in form (SYMBOL-FUNCTION T). This is with LispWorks 6.0.0 on a MacOSX Server 10.6.2 (Intel) running Swank 2010-02-14. -- Terje Norderhaug terje@in-progress.com