thodg/cl-unix-cybernetics

diff --git a/core/defs.lisp b/core/defs.lisp
index 984b1ec..9383b03 100644
--- a/core/defs.lisp
+++ b/core/defs.lisp
@@ -105,7 +105,7 @@
 ;;  Resource base class
 
 (defclass resource (standard-object)
-  ((id :type atom
+  ((id :type string
        :initarg :id
        :initform (error "Missing ID for resource.")
        :reader resource-id)
@@ -119,6 +119,8 @@
 		      :accessor probed-properties))
   (:metaclass resource-class))
 
+(declaim (ftype (function (resource) string) resource-id))
+
 (defgeneric resource-probes-properties (resource))
 
 (setq *the-resource-class* (find-class 'resource))