Direct access to Tcl_Interp->result was deprecated in 8.6
--- a/modules/tk/tk.c
+++ b/modules/tk/tk.c
@@ -76,6 +76,7 @@ char *strchr (), *strrchr ();
#endif
#define TCL_THREADS
+#define USE_INTERP_RESULT
#include <tcl.h>
#include <tk.h>