Behavior :

1 – initialize current state

2 – loop until the user's input equal to "quit"

print the current state

read a string

process a step

catch exceptions if there are some and exit the program displaying the error.

Here is the code of the operation :

operation run() :  Void raises FSMException is do  
		// reset if there is no current state
		if self.currentState == void then self.currentState := self.initialState end
		self
		from var str : String init "init"
		until str == "quit"
		loop
			stdio.writeln("Current state : " + self.currentState.name)
			str := stdio.read("give me a letter : ")
			if str == "quit" then
				stdio.writeln("")
				stdio.writeln("quitting ...")
			else 
				if str == "print" then
					stdio.writeln("")
				else	
					stdio.writeln(str)			
					stdio.writeln("stepping...")
					do
						var textRes : String
						textRes := self.currentState.step(str)
						if( textRes == void or textRes == "" )
						then
							textRes := "NC"
						end
						
						stdio.writeln("string produced : " + textRes)
					
						rescue (err : ConstraintViolatedPre)
		            		stdio.writeln(err.toString)
		            		stdio.writeln(err.message)
		            		str := "quit"
		            	rescue (err : ConstraintViolatedPost)
	            			stdio.writeln(err.toString)
	            			stdio.writeln(err.message)
	            			str := "quit"
	            		
						rescue(err : NonDeterminism)
							stdio.writeln(err.toString)
							str := "quit"	
						rescue(err : NoTransition)
							stdio.writeln(err.toString)
							str := "quit"
	            	end
				end
			end
		end
	end

In this operation, there are pre and post conditions. These are conditions checked each time the operation is called. If they are evaluated to false an exception is raised. You can choose to check them or not. The following chapter presents how to run configurations.

Behavior :

1 – Select the possible transitions.

2 – If there is none raise a NoTransition exception.

If there is more than one raise a NonDeterminism exception.

3 – If there is only one transition, call its fire operation and return its result.

// Go to the next state
	operation step(c : String) : String raises FSMException
	is do
		// Get the valid transitions
		var validTransitions : Collection<Transition> 
		validTransitions :=	outgoingTransition.select { t | t.input.equals(c) }
		// Check if there is one and only one valid transition
		if validTransitions.empty then raise NoTransition.new end
		if validTransitions.size > 1 then raise NonDeterminism.new end
		
		// Fire the transition
		result := validTransitions.one.fire
	end

Behavior :

1 – change the current state of the FSM

2 – return the produced string

// Fire the transition
	operation fire() : String is do
		// update FSM current state
		source.owningFSM.currentState := target
		result := output
	end