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Declarative Approach to Implementing Automata Classes
in Imperative Programming Languages
Artyom Astafurov, [email protected] Shalyto, SPbSUITMO
Second Spring Young Researchers’ Colloquium on Software EngineeringMay 29th 2008
Before We Start
• Automata based programming?• OOP and Automata?• Imperative?• Declarative?• Our framework• Example
What is “Automata based programming”?
OOP and Automata
Foundation
EventA()EventB()
State1 State2
State1 EventB
EventA
State2
Nesting
State1
EventB
EventA
State2
State1A State1B
EventA
EventB
Inheritance
State1
EventB
EventA
DerivedState2
State1A State1B
EventA
EventB
What is “Imperative”?
• Explicit instructions• Steps to take• Answers the question “How?”
What is “Declarative”?
• Defines the end result• Doesn’t contain steps to achieve the result• Answers the question “What?”
This HTML code
<html>
Input: <input value="Hello, world!">
</html>
Can produce…
What’s the catch?
Hybrid approach!
Imperative for functionality and logicDeclarative for the structure
or
+[InnerState(“State1A”)]public class State1{
// Events go here}
Add some reflection or instrumentalization
Result: working code that doesn’t have explicit delegation of calls to nested automatons and
has all the magic behind the inheritance implemented
Example
In a nutshell:
IpodPlayer
Sleeping PlayerMode
Play
PlayHold
public interface IAcceptsPlay{ void Play();}public interface IAcceptsPlayHold{ void PlayHold();}public interface IIpodPlayer : IAcceptsPlay, IAcceptsPlayHold{ }
public class Sleeping : State, IAcceptsPlay{
public void Play(){
//...}
}
public class PlayerMode : State, IAcceptsPlayHold{
public void PlayHold(){
//...}
}
[InitialState(“Sleeping”), InnerState(“PlayerMode”)]public class IpodPlayer : Automaton, IIpodPlayer{
// Play and PlayHold stubs go here}
More complex now:
NewPlayerMode
Paused Playing
Play
Play
public class Paused : State, IAcceptPlay{
public void Play() {
Container.SetState(“Playing”); }}
public class Playing : State, IAcceptPlay{
public void Play() {
Container.SetState(“Paused”); }}
[InitialState(“Paused”),State(“Playing”)]public class NewPlayerMode : PlayerMode{
// That’s it!}
NewIpodPlayer
Sleeping
Play
PlayHold
NewPlayerMode
Paused Playing
Play
Play
And the new player is:
[State(“PlayerMode”, “NewPlayerMode”)]public class NewIpodPlayer : IpodPlayer{
// That’s it!}
Spasibo!
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