Kermeta

package fsm;

require kermeta

using kermeta::standard

class State {
    attribute name : String
    reference transitions : Transition[0..*]#source

    operation step(c : String) : State is do
        var found : Boolean init false
        transitions.each { t |
            if not found then
                if t.input == c then
                    stdio.writeln("Transition from " + name + " to " + t.target.name + " on " + c)
                    result := t.target
                    found := true
                end
            end
        }
        if not found then
            stdio.writeln("No transition from " + name + " on " + c)
            result := self
        end
    end
}

class Transition {
    attribute input : String
    attribute output : String
    reference source : State#transitions
    reference target : State
}

class FSM {
    attribute states : State[0..*]
    reference initialState : State
    reference currentState : State

    operation run(inputs : Sequence<String>) : Void is do
        currentState := initialState
        stdio.writeln("Starting in state " + currentState.name)
        inputs.each { c |
            currentState := currentState.step(c)
        }
        stdio.writeln("Final state: " + currentState.name)
    end
}