anchor.diff:                                                         :value (env key)
                                                          :exported nil)))
   
  -(defmacro define-environment-accessor (name &optional (default '+env-default+))
  +(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)))
  
positive.code: (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+)))
      (do-iterator (binding (environment-iterator))
        (multiple-value-bind (key value) (deconstruct-environment-binding binding)
          (setf map (fset:with map key (make-instance 'environment-binding
  
negative.code: 
  (optimization-settings)
  
  (defparameter *env-default* ""
    "The value of unset environment variables.")
  
  (defclass environment-binding ()
    ((value
      :initarg :value
      :initform *env-default*
      :accessor environment-binding-value
      :type string)
     (exported-p
  