anchor.diff:         (%obj-unsetenv env name)))
       name))
   
  -(defun clear-environment (&key env)
  +(defun clear-environment (&optional env)
     "Removes all variables from an environment."
     (etypecase env
       (null
  
positive.code: (defun %obj-clearenv (env)
    (clrhash (environment-variables env)))
  
  (defun environment-variable (name &key env)
    "ENVIRONMENT-VARIABLE returns the environment variable
  identified by NAME, or NIL if one does not exist.  NAME can
  either be a symbol or a string.
  
negative.code:       (environment
         (%obj-getenv env name)))))
  
  (defun (setf environment-variable) (value name &optional env &key (overwrite t))
    (let ((value (string value))
          (name (string name)))
      (etypecase env
  