This code[1] doesn't work well in CCL. Calls upon warn-deprecated play out as so: ps> (warn-deprecated 'forth 'lisp) 0> Calling (warn-deprecated forth lisp) ; Compiler warning: In a toplevel form: Nonspecific warning ; While executing: warn-deprecated, in process repl-thread(12). <0 warn-deprecated returned nil nil ps> This can be resolved by adjusting the condition being defined: ps> (define-condition simple-style-warning (simple-warning style-warning) ()) simple-style-warning ps> (warn-deprecated 'forth 'lisp) 0> Calling (warn-deprecated forth lisp) ; Compiler warning: FORTH is deprecated, use LISP instead ; While executing: warn-deprecated, in process repl-thread(12). <0 warn-deprecated returned nil nil ps> WDYT?