This is based on the GBBOpen tutorial.
GBBOpen is an implementation of the Blackboard Design Pattern, i.e. a scheme that helps to coordinate the work of a number of so called Knowledge Source (i.e. applications) by providing a place were they can rondevous known as a blackboard. The blackboard is a set of objects that representation of the current state of the problem the system is working on (i.e. it’s a represents the problem space). Knowledge source can install triggers that fire when various events happen as the problem state changes.
In the GBBOpen tutorial, and this code, a blackboard is used by two very simple knowledge sources, start and random-walker. The only information place upon the blackboard are instances of the unit-instance class location.
The work done by these knowledge sources is coordinated by the built in control shell. We add event handlers which fire when the shell starts and as things finish up, i.e. quiescence. Upon starting we create the blackboard, and when things quiet down we print the random walk taken by the random-walker.
This example thus illustrates:
- how a blackboard consist of some number of spaces, in this case one named ‘(known-word),
- how knowledge sources are driven by event triggers (three in fact:
- control-shell-started which is used by our start KS,
- (instance-created-event location) which is used by our random-walker);
- how instances on the blackboard maybe linked to each other in a fairly elegant manner.
The ASDF system definition has two components:
- bar.lisp the actual application in bar.lisp, and
- startup.lisp a bit of junk to get things bootstrapped.
It also depends on gbbopen, and alexandria.
To run this you ought to be able to place this where your quicklisp can find it and then do: “`common-lisp (ql:quickload “gbb-one”) (gbbopen-user::go-go) “` The go-go function discards any existing blackboard and then runs the control shell. You can run go-go repeatedly, and in the comments you’ll find examples of how to do various kinds of tracing and how to displace the state of things. For example after running go-go you can display a summary of the blackboard.
GBBOpen’s modularity is a layered, like an archaeology dig. There is an old module system bundled with it, let’s call those gbbopen modules. Clever code is provided to get ASDF working for those modules. Quicklisp then works because it stands on ASDF. I don’t fully understand this clever code. It it appears broken in some scenarios. It appears that those in the know always load a file known as initialize.lisp, and you can see I load that in startup.lisp, and then I load the gbbopen module called gbbopen-user. One feature of initialize.lisp is that it provides a number of “repl commands.” I’m prejudiced against repl commands. So I haven’t given them the attention they probably deserve. I wrap the load of the initialize file in an attempt to suppress it’s tendency to change the current package.
There are some self indulgent macrolets in bar.lisp.