Index: doc/example-scripts/tk-locomotive.tcl
===================================================================
diff -u -rc2374366bcb47c70ebd33cb16c8152eba783987f -r7c692cef773e19f9da59bef6498ba673cdff468e
--- doc/example-scripts/tk-locomotive.tcl	(.../tk-locomotive.tcl)	(revision c2374366bcb47c70ebd33cb16c8152eba783987f)
+++ doc/example-scripts/tk-locomotive.tcl	(.../tk-locomotive.tcl)	(revision 7c692cef773e19f9da59bef6498ba673cdff468e)
@@ -11,6 +11,7 @@
 #
 package require Tk
 package require nx
+package require nx::trait
 
 nx::Class create Wheel {
   :property x 
@@ -84,6 +85,8 @@
 nx::Class create Locomotive {
   :property {speed 4}
 
+  :require trait nx::traits::callback
+
   :method turn {} {
     set :alpha [expr {round(${:alpha} + 360 - ${:speed}) % 360}]
     foreach i [${:c} find withtag counterweight] {
@@ -145,9 +148,9 @@
     set :c [canvas .c -width 600 -height 160 -background lightblue]
     pack ${:c}
 
-    bind ${:c} <1> [list [self] throttle]
-    bind ${:c} <2> [list [self] break]
-    bind ${:c} <3> [list [self] emergencyBreak]
+    bind ${:c} <1> [:callback throttle]
+    bind ${:c} <2> [:callback break]
+    bind ${:c} <3> [:callback emergencyBreak]
     
     ${:c} delete all
     ${:c} create rect 32 115 360 125 -fill black ;# frame