On 6 May 2013 08:22, Yanni Chiu <ya...@rogers.com> wrote: > On 05/05/13 8:31 PM, Carla F. Griggio wrote: >> >> >> I will keep experimenting with this during the next weeks, and specially >> try to compare the pros and cons with regular event handling. > > > I've always been curious to see how state machine transitions would map to > Announcements/event handling. > > >> Something cool about this approach is that the same widget could change >> its interactive behaviour on the fly by just attaching a different >> interaction state machine to it :) > > > Changing the state machine is called "subtype migration" in Shlaer-Mellor > parlance. It seems to get tricky when the supertype also has a state > machine. > > >> Also, I'm doing this for programming user interface interactions, but it >> could be useful for anything that can be modelled with a state pattern. >> >> Is there something similar out there already working? I was so eager to >> try this that I didn't look for related existing projects. > > > The PostgreSQL Client [1] (a native Smalltalk client connection to a > Postgres server) uses an internal state machine to drive the client/server > connection. It was built with the Shlaer-Mellor method [2] concepts in mind. > There was an accompanying state machine diagram drawn with the Connectors > [3] tool (the link from SqueakMap is long dead, but I could try to dig up a > copy). > > The implementation is very awkward around where the public API to make SQL > queries interacts with the underlying state machine inside the PGConnection > object. There's a loop that continues until a "good" state is reached. Then > the result is gathered from the connection object. Since the code making the > SQL query is not event-driven, nor is it part of the same state-machine > architecture of the postgres client, the result is the awkward loop. > > I'd really like to see more examples of state machine usage. > > [1] http://www.squeaksource.com/PostgresV2.html > [2] http://en.wikipedia.org/wiki/Shlaer–Mellor_method > [3] http://wiki.squeak.org/squeak/1773 > > What i often observing is that it is not matter, how good & sound the scientific concept.. when it goes to implementation it has big chances to end up with messy code, ineffective, inappropriate and therefore useless :)
That not to say that science is just waste of time.. it is to say that science alone is not enough. -- Best regards, Igor Stasenko.
