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Bison
*****

   This manual documents version 1.35 of Bison, updated 25 February
2002.

Introduction
Conditions
Copying: The GNU General Public License says

Tutorial sections:

Concepts: Basic concepts for understanding Bison.
Examples: Three simple explained examples of using Bison.

Reference sections:

Grammar File: Writing Bison declarations and rules.
Interface: C-language interface to the parser function `yyparse'.
Algorithm: How the Bison parser works at run-time.
Error Recovery: Writing rules for error recovery.
Context Dependency: What to do if your language syntax is too
Debugging: Debugging Bison parsers that parse wrong.
Invocation: How to run Bison (to produce the parser source file).
Table of Symbols: All the keywords of the Bison language are explained.
Glossary: Basic concepts are explained.
Copying This Manual: License for copying this manual.
Index: Cross-references to the text.

The Concepts of Bison

Language and Grammar: Languages and context-free grammars,
Grammar in Bison: How we represent grammars for Bison's sake.
Semantic Values: Each token or syntactic grouping can have
Semantic Actions: Each rule can have an action containing C code.
Bison Parser: What are Bison's input and output,
Stages: Stages in writing and running Bison grammars.
Grammar Layout: Overall structure of a Bison grammar file.

Examples

RPN Calc: Reverse polish notation calculator;
Infix Calc: Infix (algebraic) notation calculator.
Simple Error Recovery: Continuing after syntax errors.
Location Tracking Calc: Demonstrating the use of @N and @$.
Multi-function Calc: Calculator with memory and trig functions.
Exercises: Ideas for improving the multi-function calculator.

Reverse Polish Notation Calculator

Decls: Rpcalc Decls. Bison and C declarations for rpcalc.
Rules: Rpcalc Rules. Grammar Rules for rpcalc, with explanation.
Lexer: Rpcalc Lexer. The lexical analyzer.
Main: Rpcalc Main. The controlling function.
Error: Rpcalc Error. The error reporting function.
Gen: Rpcalc Gen. Running Bison on the grammar file.
Comp: Rpcalc Compile. Run the C compiler on the output code.

Grammar Rules for `rpcalc'

Rpcalc Input
Rpcalc Line
Rpcalc Expr

Location Tracking Calculator: `ltcalc'

Decls: Ltcalc Decls. Bison and C declarations for ltcalc.
Rules: Ltcalc Rules. Grammar rules for ltcalc, with explanations.
Lexer: Ltcalc Lexer. The lexical analyzer.

Multi-Function Calculator: `mfcalc'

Decl: Mfcalc Decl. Bison declarations for multi-function calculator.
Rules: Mfcalc Rules. Grammar rules for the calculator.
Symtab: Mfcalc Symtab. Symbol table management subroutines.

Bison Grammar Files

Grammar Outline: Overall layout of the grammar file.
Symbols: Terminal and nonterminal symbols.
Rules: How to write grammar rules.
Recursion: Writing recursive rules.
Semantics: Semantic values and actions.
Declarations: All kinds of Bison declarations are described here.
Multiple Parsers: Putting more than one Bison parser in one program.

Outline of a Bison Grammar

C Declarations: Syntax and usage of the C declarations section.
Bison Declarations: Syntax and usage of the Bison declarations section.
Grammar Rules: Syntax and usage of the grammar rules section.
C Code: Syntax and usage of the additional C code section.

Defining Language Semantics

Value Type: Specifying one data type for all semantic values.
Multiple Types: Specifying several alternative data types.
Actions: An action is the semantic definition of a grammar rule.
Action Types: Specifying data types for actions to operate on.
Mid-Rule Actions: Most actions go at the end of a rule.

Bison Declarations

Token Decl: Declaring terminal symbols.
Precedence Decl: Declaring terminals with precedence and associativity.
Union Decl: Declaring the set of all semantic value types.
Type Decl: Declaring the choice of type for a nonterminal symbol.
Expect Decl: Suppressing warnings about shift/reduce conflicts.
Start Decl: Specifying the start symbol.
Pure Decl: Requesting a reentrant parser.
Decl Summary: Table of all Bison declarations.

Parser C-Language Interface

Parser Function: How to call `yyparse' and what it returns.
Lexical: You must supply a function `yylex'
Error Reporting: You must supply a function `yyerror'.
Action Features: Special features for use in actions.

The Lexical Analyzer Function `yylex'

Calling Convention: How `yyparse' calls `yylex'.
Token Values: How `yylex' must return the semantic value
Token Positions: How `yylex' must return the text position
Pure Calling: How the calling convention differs

The Bison Parser Algorithm

Look-Ahead: Parser looks one token ahead when deciding what to do.
Shift/Reduce: Conflicts: when either shifting or reduction is valid.
Precedence: Operator precedence works by resolving conflicts.
Contextual Precedence: When an operator's precedence depends on context.
Parser States: The parser is a finite-state-machine with stack.
Reduce/Reduce: When two rules are applicable in the same situation.
Mystery Conflicts: Reduce/reduce conflicts that look unjustified.
Stack Overflow: What happens when stack gets full. How to avoid it.

Operator Precedence

Why Precedence: An example showing why precedence is needed.
Using Precedence: How to specify precedence in Bison grammars.
Precedence Examples: How these features are used in the previous example.
How Precedence: How they work.

Handling Context Dependencies

Semantic Tokens: Token parsing can depend on the semantic context.
Lexical Tie-ins: Token parsing can depend on the syntactic context.
Tie-in Recovery: Lexical tie-ins have implications for how

Invoking Bison

Bison Options: All the options described in detail,
Option Cross Key: Alphabetical list of long options.
Extension Limitations Under DOS: Bison output files extension differences
VMS Invocation: Bison command syntax on VMS.

Copying This Manual

GNU Free Documentation License: License for copying this manual.

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