anchor.diff:        (environment
          (%obj-getenv env name)))))
   
  -(defun (setf environment-variable) (value name &key env (overwrite t))
  +(defun (setf environment-variable) (value name &optional env &key (overwrite t))
     (let ((value (string value))
           (name (string name)))
       (etypecase env
  
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:        (%obj-unsetenv env name)))
      name))
  
  (defun clear-environment (&optional env)
    "Removes all variables from an environment."
    (etypecase env
      (null
  