anchor.diff:  (defun environment-to-map ()
     "Translate the posix environment of the current process into a map
   suitable for storing in `*environment*'."
  -  (let ((map (fset:empty-map +env-default-binding+)))
  +  (let ((map (fset:empty-map *env-default-binding*)))
       (do-iterator (binding (environment-iterator))
         (multiple-value-bind (key value) (deconstruct-environment-binding binding)
           (setf map (fset:with map key (make-instance 'environment-binding
  
positive.code:   (:documentation
     "Everything there is to know about an environment variable."))
  
  (define-once-global +env-default-binding+ (make-instance 'environment-binding)
    (:documentation
     "The default state for an environment binding."))
  
  (defun deconstruct-environment-binding (binding)
    "Parse a string describing an environment binding.
  
negative.code:                                                        :value (env key)
                                                         :exported nil)))
  
  (defmacro define-environment-accessor (name &optional (default '*env-default*))
    "Define a symbol macro that accesses the given environment
  variable."
    `(define-symbol-macro ,(intern (concatenate 'string "$" (string-upcase name))) (env ,name ,default)))
  