+static String modeToString ( Cell mode )
+{
+ switch (mode) {
+ case FM_SOURCE: return "source";
+ case FM_OBJECT: return "object";
+ case FM_EITHER: return "source or object";
+ default: internal("modeToString");
+ }
+}
+
+static Cell childMode ( Cell modeMeRequest, Cell modeMeActual )
+{
+ assert(modeMeActual == FM_SOURCE ||
+ modeMeActual == FM_OBJECT);
+ assert(modeMeRequest == FM_SOURCE ||
+ modeMeRequest == FM_OBJECT ||
+ modeMeRequest == FM_EITHER);
+ if (modeMeRequest == FM_SOURCE) return modeMeRequest;
+ if (modeMeRequest == FM_OBJECT) return modeMeRequest;
+ if (modeMeActual == FM_OBJECT) return FM_OBJECT;
+ if (modeMeActual == FM_SOURCE) return FM_EITHER;
+ internal("childMode");
+}
+
+static Bool compatibleNewMode ( Cell modeNew, Cell modeExisting )
+{
+ if (modeNew == FM_OBJECT && modeExisting == FM_OBJECT) return TRUE;
+ if (modeNew == FM_SOURCE && modeExisting == FM_SOURCE) return TRUE;
+ if (modeNew == FM_EITHER && modeExisting == FM_OBJECT) return TRUE;
+ if (modeNew == FM_EITHER && modeExisting == FM_SOURCE) return TRUE;
+ return FALSE;
+}
+