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.
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[jhjl] Using Tcl8.6 on Windows 7 I get an error loading the package. I tried a `'''teacup update'''` but problem persists.
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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"
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