State machines can be a powerful way to sequence execution. This is a link to a package to implement Moore type state machines in Tcl.
http://chiselapp.com/user/mangoa01/repository/mrtools/doc/tip/moore/wiki/intro.wiki
It is rather more complete than the simpler examples on the wiki, of course, at the expense of a bit more learning curve. It is large enough that it is hard to deal with as a wiki page, so I have put it in Fossil repository that I have been building for some of these types of tools.
jhjl Using Tcl8.6 on Windows 7 I get an error loading the package. I tried a teacup update but problem persists.
package require moore 1.9
unknown data type, "dict"
while executing
"relvar create StateMachine {
MachineId string
ModelName string
CurrState string
Options dict..."
(in namespace eval "::moore" script line 35)
invoked from within
"namespace eval ::moore {
variable revision 1.9
namespace export model
namespace export generate
namespace export delay
namespace ..."
(file "C:/Tcl/lib/teapot/package/tcl/teapot/tcl8/8.5/moore-1.9.tm" line 93)
invoked from within
"source -encoding utf-8 C:/Tcl/lib/teapot/package/tcl/teapot/tcl8/8.5/moore-1.9.tm"
("package ifneeded moore 1.9" script)
invoked from within
"package require moore"
("uplevel" body line 1)
invoked from within
"uplevel #0 {package require moore}"
invoked from within
"interp eval $::tkcon::OPT(exec) $args"
(procedure "::tkcon::EvalSlave" line 2)
invoked from within
"EvalAttached $cmd"