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Line 22: Put together: Given an input symbol, current state, and stack symbol, the automaton can follow a transition to another state, and optionally manipulate (push or pop) the stack. If, in every situation, at most one such transition action is possible, then the automaton is called a '''[[deterministic pushdown automaton]] (DPDA)'''. In general, if several actions are possible, then the automaton is called a '''general''', or '''nondeterministic''', '''PDA''' ~~(often just referred to as "PDA")~~. A given input string may drive a nondeterministic pushdown automaton to one of several configuration sequences; if one of them leads to an accepting configuration after reading the complete input string, the latter is said to belong to the ''language accepted by the automaton''. <!---has been said more precisely above:---Nondeterministic PDAs are able to handle situations where more than one choice of action is available.---><!---don't know what these paragraphs are supposed to mean; automata don't create 'instances' during their operation; PDAs are a theoretical model, implemetation problems aren't an issue here, see [[Earley parser]], [[LR parser]], etc., instead---:In principle, it is enough{{clarify\|date=December 2016}} to create in every such case new automaton instances that will handle the extra choices.

Pushdown automaton: Difference between revisions