YACC (Yet Another Compiler Compiler): Automating Parser Generation

Learn how YACC automates parser generation in compiler development. This guide explains YACC's input (context-free grammar), output (C code for a parser), and its role in simplifying the creation of efficient and robust parsers for programming languages.

YACC (Yet Another Compiler Compiler): Generating Parsers

What is YACC?

YACC (Yet Another Compiler Compiler) is a parser generator—a tool that automatically creates a parser (a program that analyzes the syntax of code) for a given context-free grammar (CFG). The grammar defines the programming language's structure. YACC is especially useful for building compilers because it automates a significant portion of the parser development process. YACC typically generates a parser conforming to LALR(1) (Lookahead LR) grammar rules.

How YACC Works

YACC takes a CFG (specified in a YACC-formatted file, typically with a `.y` extension) as input and generates a C program (usually named `y.tab.c`) as output. This generated C code acts as a parser for your specified grammar. The process also generates additional files:

  • y.tab.c: The C source code for the parser.
  • y.tab.h: Header file with declarations for the parser.
  • file.output: Contains the parsing tables.

This C program is compiled by a C compiler into an executable parser.

The YACC Process

  1. Provide the Grammar: The input to YACC is a file specifying the grammar in YACC format.
  2. YACC Compilation: YACC processes the grammar and generates the parser (C code).
  3. C Compilation: A C compiler compiles the generated C code.
  4. Executable Creation: The result is an executable parser that will be able to parse code according to the rules defined in the grammar.

YACC and Parser Functions

The parser generated by YACC includes a crucial function called yyparse(). This function drives the parsing process. It uses another function, yylex(), to obtain tokens (the basic building blocks of the language) from the lexical analyzer (a separate program responsible for identifying tokens in the source code).