;first example, this one works fine

(ns foo)

(defn print-extension
    [path]
    (println
        (org.apache.commons.io.FilenameUtils/getExtension path
    ))
)

;;invocation below
;lein repl
; (load-file "/home/john/get-extension.clj")
;(/foo/print-extension "/home/john/get-extension.clj") ; gives "clj", it is OK.