statemachine

Statemachine, also called a state machine, is a model of computation and behavior used to describe systems that can exist in a finite number of states. The core idea is that the system moves between states in response to events or inputs, performing actions during transitions or while in states. A typical statemachine includes a set of states, a start state, a set of transitions between states, and a set of events or inputs that trigger transitions. Some formulations also include outputs or actions associated with states or transitions.

Finite state machines are a common subset of statemachines, characterized by a finite number of states. In automata theory, deterministic finite automata have exactly one transition for each input in a given state, while nondeterministic finite automata may have several possible transitions for the same input. In sequential logic and software design, two related concepts are Mealy machines, where outputs depend on both state and input, and Moore machines, where outputs depend only on the current state.

State machines are typically represented by state diagrams or transition tables. They are used to model and implement behavior in a wide range of domains, including user interfaces, communication protocols, control systems, compilers, and embedded software. Example forms include simple control flows such as a traffic light (states like Green, Yellow, Red with timer-based transitions) or a door access system with states Locked and Unlocked governed by input events.

Implementation strategies vary from table-driven and switch-based code to event-driven architectures. In hardware, statemachines are implemented with flip-flops and logic gates; in software, they are realized with variables that hold the current state and a transition function. Benefits include clarity, modularity, and easier verification; downsides can include state explosion as system complexity grows and, for some problems, inadequate memory of past events.