Formal Languages Questions Medium
Top-down parsing and bottom-up parsing are two different approaches used in the analysis of formal languages. The main difference between them lies in the direction in which the parsing process proceeds.
Top-down parsing, also known as predictive parsing, starts from the root of the parse tree and works its way down to the leaves. It begins with the start symbol of the grammar and tries to match it with the input string by applying production rules in a leftmost derivation. This approach uses a recursive descent parsing technique, where each non-terminal symbol is associated with a parsing function. Top-down parsing is generally easier to implement and understand, but it may suffer from left recursion and backtracking issues.
On the other hand, bottom-up parsing starts from the input string and builds the parse tree from the leaves up to the root. It uses a shift-reduce parsing technique, where the input symbols are shifted onto a stack until a production rule can be applied to reduce them. Bottom-up parsing is more powerful and can handle a wider range of grammars, including left-recursive and ambiguous grammars. However, it can be more complex to implement and may require additional mechanisms like lookahead or conflict resolution strategies.
In summary, the main difference between top-down parsing and bottom-up parsing is the direction in which the parsing process proceeds. Top-down parsing starts from the root and moves down to the leaves, while bottom-up parsing starts from the input string and builds the parse tree from the leaves up to the root.