Stacks in Shift-Reduce Parsing

Shift-reduce parsing is a bottom-up parsing technique commonly used to analyze computer languages by reading the input from left to right. It starts with an empty parse stack and a buffer containing the input string. The parser shifts input symbols onto the stack until it recognizes a piece of the grammar's right-hand side. At this point, it reduces the right-hand side to its left-hand side, which is the next symbol on the stack.

Stacks are the primary data structure used during shift-reduce parsing because they provide an efficient way to keep track of the parser's state. The parse stack contains the symbols that the parser has recognized so far, and the input buffer contains the remaining symbols that need to be parsed. The stack allows the parser to maintain a history of the symbols it has recognized, which is used to determine which production rule to apply next.

When a shift-reduce parser encounters a terminal symbol, it shifts it onto the stack. This means that the symbol is recognized and can be used in future reduction steps. When a parser recognizes a set of symbols that match the right-hand side of a production rule, it reduces the symbols to the left-hand side of the rule. This means that the symbols are replaced by a single nonterminal symbol that represents the entire right-hand side.

In summary, stacks are used during shift-reduce parsing to maintain the parser's state and keep track of the symbols that have been recognized so far. They allow the parser to efficiently shift input symbols onto the stack and reduce them to nonterminal symbols that represent the grammar's rules.