Parsergenerator

Parser generators, also known as parser generators, are software tools that produce parsers from formal grammar specifications. A user writes a grammar describing tokens and the syntactic rules of a language or data format. The generator processes the specification and emits source code for a parser in a target programming language. The resulting parser analyzes input streams, builds parse trees or abstract syntax trees, and reports syntax errors with location information.

Most practical parsers are generated for deterministic grammars and commonly implement LR, LALR, or LL parsing strategies. Yacc and Bison produce LALR parsers, while ANTLR targets LL-type parsing with adaptive lookahead. Grammar designers may need to resolve ambiguities, specify operator precedence and associativity, and sometimes rewrite left-recursive rules for LL parsers. Tokenization is usually performed by a separate lexer, though some tools integrate scanning and parsing.

Generated code often includes hooks or semantic actions to build an AST or perform semantic checks as the parse proceeds. The tool may rely on a runtime library for token streams, error reporting, and parse-tree facilities. Users typically supply the grammar plus a small amount of host-language code for actions; the generator then emits compilable code that uses that runtime.

Common examples of parser generators are Yacc, Bison, ANTLR, and JavaCC. They are used in compilers, interpreters, configuration file parsers, data validators, and data-interchange processors. The main trade-offs involve expressiveness versus complexity, handling of ambiguity, and the quality of error messages.