Dining philosophers can be implemented in ESL so that each
philosopher is an actor that needs to grab two chopsticks in order
to eat. A co-ordination mechanism must be used in the form of data
locks so that two chopsticks are grabbed at a time, otherwise the
philosophers can deadlock and starve. ESL can turn an execution
history into a filmstrip that is shown as a picture. Dragging the
marker left and right moves forward and backward through the
execution showing that no deadlock occurs.
Click on the image on the right to load the example in EDB.
Pacman is a game where the player controls the movement through
a maze of the yellow pacman who wants to eat all the food, and where
the system controls the ghosts who are seeking to eat the pacman.
All the ghosts are actors who move independently of the pacman that
is controlled by the user via the mouse. The ghosts implement a
suitable strategy by inspecting the current state of the world and
making a decision about their next move.
Click on the image on the right to load the example in EDB.
A road junction is controlled by a pair of traffic lights. Cars
travel with greater frequency right to left and therefore they
should be given priority. However, the lights should monitor the
situation so that the queue from the left does not become too long.
This example shows how ESL can be used to implement data monitors
where the traffic lights are actors and monitors are actors that
trigger changes based on the execution history of the junction
queues.
Click on the image on the right to load the example in EDB.
ESL can be used to define a simulation. A shop wishes to try out
different arrangements of of tills and assistants based on
simulations of customer behaviour. Customers enter the shop and may
seek help choosing goods before waiting at a queue to pay. If a
customer waits too long for assistance or waits too long in a queue
at a till then they will abandon their purchase and leave the shop.
EDB is used to create a dashboard that shows the current state of
each shopper during their visit to the shop.
Click on the image on the right to load the example in EDB.
Segregation is a classic multi-agent simulation showing what happens in
a typed society when there is slight bias towards co-locating with
agents of the same type. The society starts of with randomly distributed
agents typed red and blue. If the location of an agent is surrounded by
agents of a different type then they will move to a random unoccupied
location. Given a slight bias towards moving from a location, the simulation
shows that the society becomes segregated as shown in the resulting pattern
on the right.
Click on the image on the right to load the example in EDB.
Predator-prey is a typical multi-agent application with two types
of agent. A predator is trying to catch a prey in a world that contains
obstacles and places for the oprey to hide. In the example, the wolves
are trying to catch the sheep who can hide behind rocks. ESL runs the
scenario and builds a filmstrip of the states of the game. Once
completed EDB displays the filmstrip that can be played forwards and
back to see how the prey evaded capture (or not!).
Click on the image on the right to load the example in EDB.
ESL supports integration with Java so that third-party libraries such
as graphics can easily be integrated. In addition, EDB knows about particular
Java interfaces so that a Java graphics component can be created within
an ESL application and then displayed as an EDB tab as shown on the right.
The application represents balls as ESL actors that check the world for
collisions against the walls and other actors. The application is controlled
using Swing buttons that communicate with ESL when they are pressed.
Click on the image on the right to load the example in EDB.
ESL is a functional language that makes it easy to represent structured data.
In addition, EDB integrates with a number of external libraries for data visualisation.
The example shows a graph-colouring algorithm that first colours the graph and
then displays it using GraphViz.
Click on the image on the right to load the example in EDB.
Map/Reduce is a good example of data processing that can be implemented using
concurrent processes. Data from many different sources is processed in parallel
and given a key. Data with the same keys are then merged and finally reduced to
produce a result. The independence of the initial data and then of the keys
provides scope for increasing the efficiency of producing the result.
Click on the image on the right to load the example in EDB.
Termites is a nice example of emergent behaviour. The forest contains randomly distributed twigs.
Termites like twigs and seek them out by moving at random. A termite will only pick up a twig if it not bounded by
other twigs. Once it has picked up a twig, a termite will move randomly until it finds a location that
is surrounded by several twigs. Then the termite drops the twig and starts over. Over time, the termites
tidy the forest and produce piles of twigs, even though they have no knowledge of their overall
collaborative task.
Click on the image on the right to load the example in EDB.
