. Process of determination whether a string can be generated by a grammar
. Parsing falls in two categories:
- Top-down parsing:
Construction of the parse tree starts at the root (from the start symbol) and proceeds towards leaves (token or terminals)
- Bottom-up parsing:
Construction of the parse tree starts from the leaf nodes (tokens or terminals of the grammar) and proceeds towards root (start symbol)
Parsing is the process of analyzing a continuous stream of input (read from a file or a keyboard, for example) in order to determine its grammatical structure with respect to a given formal grammar. The task of the parser is essentially to determine if and how the input can be derived from the start symbol within the rules of the formal grammar. This can be done in essentially two ways:
. Top-down parsing - A parser can start with the start symbol and try to transform it to the input. Intuitively, the parser starts from the largest elements and breaks them down into incrementally smaller parts. LL parsers are examples of top-down parsers. We will study about these in detail in the coming slides.
. Bottom-up parsing - A parser can start with the input and attempt to rewrite it to the start symbol. Intuitively, the parser attempts to locate the most basic elements, then the elements containing these, and so on. LR parsers are examples of bottom-up parsers. We will study about these in detail in the coming slides.
