When using Gnocl widgets only a single callback script is permitted. This differs somewhat to the underlying Gtk bindings api which allows for a chain of callback functions to be defined.
Rather than trying to produce a convoluted means of setting complex callbacks in C, simple changes can be made during application runtime because Tcl, as a dynamic language, allows everything to be reconfigurable.
Using a simple procedure which takes three arguments: the name of the procedure to be modified, the script modifications and a flag specifying append or prepend, the following proof of concept script can created.
# !/bin/sh
# the next line restarts using tclsh \
exec tclsh "$0" "$@"
proc p1 {str} { puts $str }
proc procModify {proc script {mode -append} } {
set args [info args $proc]
set body [string trim [info body $proc]]
set box
if { $mode == "-prepend" } {
set body $script\n$body
} else {
set body $body\n$script
}
proc $proc $args $body
}
procModify p1 "puts DONE!"
procModify p1 "puts READY!" -prepend
p1 HI
