The code below returns "lx64fsl" in CCL, "fas" in CLISP, and "fasl" in SBCL, but returns "lisp" in ABCL. I think it should return "abcl" in ABCL. $ java -jar abcl-1.7.1.jar Armed Bear Common Lisp 1.7.1 Java 1.8.0_272 Oracle Corporation OpenJDK 64-Bit Server VM Low-level initialization completed in 0.586 seconds. Startup completed in 1.336 seconds. Type ":help" for a list of available commands. CL-USER(1): (pathname-type (compile-file-pathname (make-pathname :name "foo" :type "lisp") :output-file (make-pathname :name "bar"))) "lisp" CL-USER(2):