You can use proc command in Tcl to replace existing commands and procedures, which gives you the possibility to implement different behaviour. An example that

You can use proc command in Tcl to replace existing commands and procedures, which gives you the possibility to implement different behaviour. An example that shows this: ~$ tclsh % rename while origwhile % proc while {args} { puts stderr "Debug: invoked while with arguments $args" # do anything you want here uplevel 1 origwhile $args } % set i 0 % while {$i < 5} {puts $i; incr i} Debug: invoked while with arguments {$i < 5} {puts $i; incr i} 0 1 2 3 4 % And in Forth the dictionary is searched backwards for a word (starting with the most recent definitions), so you can similarly override words. Powerful!