One of the key concepts in computer programming is the idea of state, essentially a snapshot of the measure of various conditions in the system. Most programming languages require a considerable amount of state information in order to operate properly - information which is generally hidden from the programmer. For a real-world example, consider a three-way light switch. An ordinary switch turns on a light when it's in the "up" position, but in a three-way switch the "up" position could be on or off, depending on the state or "configuration" of the other switch, which is likely out of view.
In fact, the state is often hidden from the computer's hardware as well, which normally has no idea that this piece of information determines program state, while that piece is a temporary variable and will soon be discarded. This is a serious problem, as the state information needs to be shared across multiple processors in parallel processing machines. Without knowing which state is important and which isn't, most languages force the programmer to add a considerable amount of extra code to indicate which data and parts of the code are important in this respect.
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