Class Grammar

Abstract base class for grammar implementations in the Earley parser.

Inheritance

object

Grammar

ContextFreeGrammar

Inherited Members

object.Equals(object)

object.Equals(object, object)

object.GetHashCode()

object.GetType()

object.MemberwiseClone()

object.ReferenceEquals(object, object)

Namespace: EarleyParser

Assembly: EarleyParser.dll

Syntax

public abstract class Grammar

Remarks

Provides the foundation for both context-free and linear indexed grammars.

Key features:

1. Grammar Structure:
   • Dictionary of production rules indexed by left-hand side
   • Support for both context-free and linear indexed rules
   • Special symbols for grammar operations (Gamma, Start, Epsilon, Star)
2. Grammar Analysis:
   • Detection of recursive non-terminals
   • Analysis of grammar reachability
   • Support for parts of speech vocabulary
3. Rule Management:
   • Dynamic rule addition and removal
   • Support for tentative grammar modifications
   • Validation of grammar structure

Usage:

• Instantiate either ContextFreeGrammar or LinearIndexedGrammar
• Load rules from grammar files (see CFGExample.txt and LIGExample.txt)
• Load parts of speech from vocabulary.json

The grammar class is the foundation of the parsing system, defining the language structure that the Earley parser will recognize.

Constructors

Grammar(IEnumerable<Rule>)

Initializes a new instance of the Grammar class.

Declaration

public Grammar(IEnumerable<Rule> rules1)

Parameters

Type	Name	Description
IEnumerable<Rule>	rules1	The collection of rules to initialize the grammar with.

Fields

EpsilonSymbol

Gets the epsilon symbol used for empty productions.

Declaration

public const string EpsilonSymbol = "Epsilon"

Field Value

Type	Description
string

GammaSymbol

Gets the gamma symbol used in grammar operations.

Declaration

public const string GammaSymbol = "Gamma"

Field Value

Type	Description
string

PartsOfSpeech

Gets or sets the set of valid parts of speech.

Declaration

public static HashSet<string> PartsOfSpeech

Field Value

Type	Description
HashSet<string>

Rules

Gets the dictionary of production rules indexed by their left-hand side.

Declaration

public readonly Dictionary<string, List<Rule>> Rules

Field Value

Type	Description
Dictionary<string, List<Rule>>

Remarks

Rules are organized into a dictionary with their Left Hand Side as key. For Linear Indexed Grammar, multiple Context Free rules may be generated for one LIG rule. Only includes CFG Rules reachable from START nonterminal.

StarSymbol

Gets the star symbol used in grammar operations.

Declaration

public const string StarSymbol = "*"

Field Value

Type	Description
string

StartSymbol

Gets the start symbol used to begin parsing.

Declaration

public const string StartSymbol = "START"

Field Value

Type	Description
string

Methods

FindAllRecursiveNonterminals()

Finds all recursive non-terminals in the grammar.

Declaration

public HashSet<string> FindAllRecursiveNonterminals()

Returns

Type	Description
HashSet<string>	A set of non-terminals that are recursive.

FindRecursiveNonterminal(string, string, HashSet<string>)

Determines whether a non-terminal is recursive.

Declaration

public bool FindRecursiveNonterminal(string targetNT, string currentNT, HashSet<string> visited)

Parameters

Type	Name	Description
string	targetNT	The non-terminal to check for recursion.
string	currentNT	The current non-terminal being examined.
HashSet<string>	visited	Set of non-terminals already visited.

Returns

Type	Description
bool	True if the target non-terminal is recursive; otherwise, false.

GetRules()

Gets all rules in the grammar.

Declaration

public List<Rule> GetRules()

Returns

Type	Description
List<Rule>	A list of all rules in the grammar.

ToString()

Returns a string representation of the grammar.

Declaration

public override string ToString()

Returns

Type	Description
string	A string containing all rules and their count.

Overrides

object.ToString()