My State Machine

• I want to have a puzzle where the user must select items AB+C
  • This is a regular expression that describes the solution to the puzzle.
  • They must tap item A, followed by 1 or more taps to item B, followd by a tap to item C.
• A state machine describes a set of states that the solution to the puzzle could be in
  • A start state where I have not seen valid input.
  • State 1, where I have seen an A.
  • State 2, where I have seen at least AB, but perhaps more B inputs
  • State 3, where I have seen AB+C.
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• State 0 is called the start state and is indicated by an arrow pointing to it.
  • We always start in state 0.
  • On a total fail or reset we will go back to state 0.
• State 3 is called the accepting state or final state and is indicated by the double circle.
  • If we reach state 3, the puzzle has been solved.
  • We could go back to the start state.
  • Or we could remove or disable the puzzle.
• The state machine has a set of inputs, in this case A,B,C,D
• We generally define a set of transitions that occur
  • It is a tuple (state, input) -> new state
  • We draw this as an arrow from one state to another with a label
  • So if we encounter an A in state 0, we transistion to state 1.
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  • We also define a default transition.
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  • So if we are in state 0, we can progress to state 1 by input A, otherwise we remain in state 0.
• So the final state table is
  • 

    State/Input	A	B	C	D
    0	1	0	0	0
    1	1	2	0	0
    2	1	2	3	0

• We need the following
  • Transition logic that interprets the state table.
  • Possible logic that is triggered on entering a state.
  • Possible logic that is triggered on exiting a state.
• My implementation.
  • I have a set of items, that will provide "input" on collision.
  • Detecting it is somewhat of a pain
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  • Note, I am using a variable input to record the input
• I then built state transition logic
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  • This takes the input and the state and computes the new state.
• You could have pre-state change or post-state change logic built in.
  • In my case, I chose to have post state change logic.
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