In computer science, a parser is a program that analyzes a string of symbols, called the input, according to a set of rules. The parser breaks the input down into smaller units and determines if the input follows the rules of a specific grammar. If it does, the parser outputs a parse tree, which shows the grammatical structure of the input.
There are three main types of parsing techniques:
- Top-down parsing: This type of parsing starts from the start symbol of the grammar and tries to match the input string against the right-hand side of the grammar productions. It works in a predictive manner, trying to guess what the next input symbol will be based on the current state of the parse.
- Bottom-up parsing: This type of parsing starts from the input string and tries to build up a parse tree by matching the input symbols against the left-hand side of the grammar productions. It works in a data-driven manner, making decisions based on the symbols that have already been seen.
- Universal parsing: This type of parsing can be used to parse any string, regardless of the grammar. However, it is not very efficient for most grammars.
These are just the basic parsing techniques. There are many other parsing algorithms that have been developed, each with its own advantages and disadvantages. The choice of parsing technique depends on the specific needs of the application.