tkhoa2711

(defun flatten (lst)
  "flatten nested list"
  (labels ((flatten-rec (lst acc)
             (cond ((null lst) acc)
                   ((atom lst) (cons lst acc))
                   (t (flatten-rec
                       (car lst)
                       (flatten-rec (cdr lst) acc))))))
    (flatten-rec lst nil)))

tkhoa2711

(defun print-list (list)
  (format t "~{~A ~}~%" list))

tkhoa2711

import threading

# A thread-safe implementation of Singleton pattern
# To be used as mixin or base class
class Singleton(object):
    
    # use special name mangling for private class-level lock
    # we don't want a global lock for all the classes that use Singleton
    # each class should have its own lock to reduce locking contention
    __lock = threading.Lock()