Parse

Parse is the process of analyzing a sequence of tokens to determine its grammatical structure with respect to a given formal grammar. In linguistics, parse refers to determining the syntactic structure of a sentence, often represented as a parse tree or dependency structure. In computer science, parsing is the process of reading input data and building a data structure that describes its grammar or structure.

A parser works with a grammar, typically defined by a formal grammar such as a context-free grammar. The input is first tokenized by a lexer, then parsed to produce a tree or other data representation. Parsers are implemented as software components in compilers, interpreters, and data-processing systems. They translate text or streams into structured representations that can be further analyzed or executed.

Common parsing strategies include recursive-descent (a family of top-down parsers), LL parsers, and LR and LALR parsers (bottom-up). Parsing with parsing expression grammars (PEG) is another approach. Parsers may perform error reporting and recovery when input does not match the grammar, and may support incremental or streaming parsing for large or ongoing inputs.

Applications of parsing span multiple domains. In software development, parsers support compilers and interpreters and enable processing of data formats such as JSON, XML, and programming languages. In natural language processing, parsing helps reveal sentence structure for downstream tasks like understanding and translation. Parsing also underpins data extraction from text, logs, and configuration files.