Robby,
Thanks
Not at all opaque. I was experimenting with that earlier this afternoon,
as below.
Actuallly, the way you phrased it helps clarify something I was struggle
with.
A very useful and valuable suggestion. I think that may very well be
plan B.
R./
Zack
(define (nextproc)
;need an intermediate function, or it will replace prior mark
(tail-calling
(list
(with-continuation-mark 'state '(S2 beforeproc afterproc) ((λ ()
(printf
"in S2 ~A\n" (continuation-mark-set->list
(current-continuation-marks) 'state)))))
(with-continuation-mark 'state '(S3 beforeproc afterproc) ((λ ()
(printf
"in S3 ~A\n" (continuation-mark-set->list
(current-continuation-marks) 'state)))))))
(with-continuation-mark 'state '(S1 beforeproc afterproc) (nextproc))
On Sat, Dec 31, 2011 at 9:03 PM, Robby Findler wrote:
I'm not sure if the web-server supports continuation marks or not, but
if it does, you could use continuation marks to note what the exit and
entry operations are, and then when you would do a continuation jump,
first grab the continuation marks from one side, do the jump, grab the
continuation marks from the other side, and then explicitly do the
actions that the marks have recorded should be done. (Let me know if
that is too opaque ...)
Robby
On Sat, Dec 31, 2011 at 7:56 PM, Galler <[email protected]>
wrote:
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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