anchor.diff:    ((variables :initarg :variables
                 :initform (make-hash-table :test #'equal)
                 :accessor environment-variables)))
  -
  -(defun %envar (env name)
  -  (gethash name (environment-variables env)))
  -
  -(defun (setf %envar) (value env name)
  -  (setf (gethash name (environment-variables env))
  -        value))
  -
  -(defun %remvar (env name)
  -  (remhash name (environment-variables env)))
   
   (defun environment-variable (name &key env)
     "ENVIRONMENT-VARIABLE returns the environment variable
  
positive.code:       (null
         (isys:%sys-unsetenv (string name)))
        (environment
         (%remvar env name))))
    (values name))
  
  (defun environment ()
  
negative.code:        (isys:%sys-setenv (string name) value overwrite))
        (environment
         (when (or overwrite
                   (null (nth-value 1 (gethash name (environment-variables env)))))
           (setf (gethash name (environment-variables env))
                 value)))))
    value)
  
  (defun makunbound-environment-variable (name &key env)
  