Re: SNL: state change statement in entry block

[Eric Williams <ecwilliams@lbl.gov>]

It turned out to be useful in the case I was working on.  Thanks, and thanks for the explanation.

--

eric

On Sat, Mar 14, 2015 at 5:57 PM, Benjamin Franksen <benjamin.franksen@helmholtz-berlin.de> wrote:

Hi Andrew

Since version 2.1 the sequencer deviates from the Mealy Machine model, in that
you can say

        state other_state;

in the middle of an action block. I called this a "state change statement"
(and it really is a statement, not an _expression_). It is only allowed inside
transitions, not in entry or exit blocks. This can be useful in situations
where determining the next state cannot be expressed as a closed formula in
SNL, for instance if it involves iteration.

Cheers
Ben

Am Samstag, 14. März 2015, 03:06:12 schrieb Johnson, Andrew N.:
> The SNL compiler implements a version of the well-known finite state machine
> (FSM) known as a Mealy Machine. Each SNL state set in a program corresponds
> to a single FSM, comprising a set of states connected by transitions, which
> are made up of input (when) conditions and output actions. An entry block
> just provides a set of actions (i.e. FSM outputs) to be executed whenever
> its state is entered. Action sequences cannot contain state changes, those
> are determined only by the transition conditions which trigger the actions.
>
> If you discover that an action sequence needs to change the transition it's
> implementing, you will usually have to add one or more states and
> transitions to properly model and code the result. The advantage of state
> programming is that (in theory) for any series of inputs you can determine
> exactly how the machine will respond. In practice state programs with lots
> of states can be complex beasts to follow; drawing up a corresponding state
> transition diagram can help in these circumstances, but I wouldn't try to
> detail all of the actions on the diagram.
>
> HTH,
>
> - Andrew
>
> > On Mar 13, 2015, at 7:36 PM, Eric Williams <ecwilliams@lbl.gov> wrote:
> >
> > I had put a state change statement in the entry block of one of my states
> > and the 2.2.1 compiler kicked it out.  Evidently it only allowed them in
> > transition blocks.  I re-arrange my code to get around the restriction
> > but I was curious: What is the problem with having a state change
> > statement in an entry block? --
> > Eric Williams
> > ALS Controls, LBL

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