YACC

Yacc is a grammar parser; it reads text and can be used to turn a sequence of words into a structured format for processing.

This means that if yacc would have to read two tokens before it knew which action to take, it would be unable to parse this grammar.

Here's a simple example of a program that can be written in a page of yacc and a half-page of lex code.

In some cases, Yacc fails to produce a parser when given a set of specifications.

Throughout these articles, the names "lex" and "yacc" will be used to include also flex and bison, the GNU versions of these utilities.

Yacc allows you to refer to the components of an expression by symbolic names.

This data type is a C union object, and is declared in the first section of a yacc file using a %union declaration.

The first section of a yacc file defines the objects that the parser will manipulate and generate.

Normally we would use the compiler generator tools lex and yacc to build that part of the program which recognizes an arithmetic expression.

Lex and yacc are a matched pair of tools.

Yacc provides a general tool for imposing structure on the input to a computer program.

The general way this is done is to define a data type to contain objects that yacc will be manipulating.

For instance, code in many programming languages can be read using lex and yacc.

Yacc is designed to work with the output of Lex, although you can write your own code to fill that gap.

Lex and yacc can be used to parse fairly simple and regular grammars.

One of the best things you can do to learn more about lex and yacc is to write a few toy programs.

Yacc takes sets of tokens and assembles them into higher-level constructs, analogous to sentences.

This is where yacc comes in: yacc lets you describe what you want to do with tokens. A yacc grammar tends to look sort of like this

Those tools we look at here do so, as does the popular compiler development tool YACC (and its variants).

Yacc files, like lex files, come in sections separated by %% markers.

External DSLs build a new language grammar, requiring tools like lexx and yacc or Antlr.

JavaCC, like YACC, is designed to speed the process of developing parser logic for languages.

Lex and yacc are very good at parsing reasonably simple file formats.

Yacc then generates a function to control the input process.

Yacc: This tool is standard on most UNIX operating systems.

This grammar is ambiguous; yacc can't figure out what's going on.

Lex and yacc are tools for building programs.

The biggest limitation is that yacc is limited to one token of lookahead.

By using the lex and yacc tools, you can build a parsing engine that processes text according to specific rules.

What are lex and yacc, and why do people refer to them together?

In this tutorial, you'll examine how to use lex and yacc, first to build a calculator.

Programs using yacc, but not lex, are rarer.

In fact, while lex and yacc are almost always mentioned in the same breath, they can be used separately.

This is where the UNIX lex and yacc tools are useful.

Most people never need to know what lex and yacc do.

One thing you'll find if you play around a bit is that lex and yacc can be confusing to troubleshoot.

The code provided should work in all major versions, such as MKS yacc.

While Yacc cannot handle all possible specifications, its power compares favorably with similar systems;

When yacc is run with the -d option, it generates a header file defining constants. Thus, our earlier lex example using

Yacc would create a header file (called y. tab. h by default) containing a line something like

Yacc can look ahead one character, though. So