Sorry, should have included a brief example.
Here's an example of what I've implemented, which is just Harel's
hierarchical state machines
You can create a Hierarchical State Machine by defining individual nodes
in a flat file, as below.
each node has 6 keyword parameters , state, parent, entry, init, exit,
and a handler.
The machine is very much like a web-server. It receives a signal (akin
to a request), processes the signal which may cause a change internal
state, and returns a continuation to be invoked when the next signal is
presented.
The new signal is the argument provided to this continuation at
invocation.
In the stateful server, the HSM continuation is closed over by the PLT
Server's external continuation (reified by send/suspend)
In the stateless version, I would replace the HSM continuation with the
PLT server's continuation (reified by send/suspend).
I can't do that right now because the continuation is in the scope of
the dynamic-wind function, which is an unsafe place to capture
continuations for #lang web-server
The dynamic wind is used as follows:
At present, the nodes are brought into the correct tree-like dynamic
extent by a recursive function which invokes dynamic-wind.
Note that the handler code supports jumping to another state (trans 'S2
'S3).
Trans invokes a continuation reified earlier associated with state S3.
In this case, the invocation of the continuation calls the exit actions
of state S2 and the entry actions of S3.
That's where the dynamic-wind comes in. Its necessary for transitions
between states and but used for anything else.
That's why I think an overridden call/cc-dynamic-wind and dynamic wind
would be sufficient.
(defnode
#:state 'S2
#:parent 'Top
#:entry (λ () (I-TLL:entry-start-TLL))
#:init (lambda () (trans 'S2 'S3))
#:exit (λ () (I-TLL:exit-secure-TLL))
#:handler (λ (signal)
(cond
[(signal-eq? signal "main") (trans 'S2 'S3)]
[(signal-eq? signal "info") (trans 'S2 'S4)]
[(signal-eq? signal "about") (trans 'S2 'S5)]
[(signal-eq? signal "item") (trans 'S2 'S6)]
[(signal-eq? signal "field") (trans 'S2 'S7)]
[(signal-eq? signal "dispatch") (trans 'S2 'S8-3)]
[(signal-eq? signal "burden") (trans 'S2 'S8-2)]
[(signal-eq? signal "planning") (trans 'S2 'S8-1)]
[(signal-eq? signal "failentry") (trans 'S2 'S3)]
[else #f])))
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