gi
Class LR0_Grammar

java.lang.Object
  gi.Lexicon
      gi.Grammar
          gi.LR0_Grammar

Direct Known Subclasses:

LR1_Grammar, SLR1_Grammar

public class LR0_Grammar

extends Grammar

This class implements an LR(0) parser around a Grammar. The parser adapts to changes in the underlying Grammar. Semantics in a phrase are evaluated during a bottom-up parse, from left to right after all subtrees rooted in the phrase have been constructed. Attributes throughout the phrase are available during evaluation. LR(0) parsing is not very practical, since it ignores lookahead information and is easily confused, but it forms a basis around which SLR(1) and LR(1) parsers are constructed.

Version:

1.2

Author:

© 1999-2004 Craig A. Rich <carich@csupomona.edu>

Nested Class Summary

(package private) static class	LR0_Grammar.Context This class implements an LR(0) Context.
(package private) static class	LR0_Grammar.Contexts This class implements a set of LR(0) Contexts.

Nested classes inherited from class gi.Grammar

Grammar.ParseTree, Grammar.Production, Grammar.Semantics

Nested classes inherited from class gi.Lexicon

Lexicon.Alphabet, Lexicon.Concatenation, Lexicon.Exception, Lexicon.Expression, Lexicon.Match, Lexicon.NonMatch, Lexicon.PosixClass, Lexicon.Range, Lexicon.Repetition, Lexicon.Set, Lexicon.Singleton, Lexicon.Stack, Lexicon.UnicodeCategory, Lexicon.Union

Field Summary

(package private) static Object	S$ The augmented start symbol.
(package private) Lexicon.Stack	states The states through which this LR(0) parser transitions.
(package private) Lexicon.Stack	trees The parse trees through which this LR(0) parser transitions.

Fields inherited from class gi.Grammar

CONFLICT, FIRST_FOLLOW, P, PARSE_TREE, S, SYNTAX

Fields inherited from class gi.Lexicon

$, debug, LEXICAL, TERMINALS, VERBOSE

Constructor Summary

protected	LR0_Grammar() Constructs an LR(0) parser around a new empty Grammar.
protected	LR0_Grammar(Grammar G) Constructs an LR(0) parser around an existing Grammar.

Method Summary

(package private) LR0_Grammar.Contexts	closure(LR0_Grammar.Contexts C) Computes the reflexive transitive closure of a set of LR(0) Contexts under empty transition.
(package private) Lexicon.Set	expected(LR0_Grammar.Contexts C) Computes the terminals expected in a set of LR(0) Contexts.
(package private) LR0_Grammar.Contexts	initial() Computes the initial state of the LR(0) DFA.
(package private) Object	interpret(LineNumberReader source) Interprets a source character stream by LR shift-reduce ascent.
(package private) Grammar.Production	parse(LR0_Grammar.Contexts C, Object a) Computes the Production to use in a reverse rightmost derivation.
String	toString() Returns the string representation of this parser, specifically "LR(0)".
(package private) LR0_Grammar.Contexts	transition(LR0_Grammar.Contexts C, Object X) Computes a transition from a set of LR(0) Contexts on a symbol.

Methods inherited from class gi.Grammar

first, first, first, follow, grab, interpret, nonterminal, put, put, terminal

Methods inherited from class gi.Lexicon

expression, interpret, interpret, interpret, interpret, interpret, interpret, put, word

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, wait

Field Detail

S$

static final Object S$

The augmented start symbol.

states

final Lexicon.Stack states

The states through which this LR(0) parser transitions.

trees

final Lexicon.Stack trees

The parse trees through which this LR(0) parser transitions.

Constructor Detail

LR0_Grammar

protected LR0_Grammar()

Constructs an LR(0) parser around a new empty Grammar.

LR0_Grammar

protected LR0_Grammar(Grammar G)

Constructs an LR(0) parser around an existing Grammar.

Parameters:

G - the Grammar around which the parser is constructed.

Method Detail

closure

LR0_Grammar.Contexts closure(LR0_Grammar.Contexts C)

Computes the reflexive transitive closure of a set of LR(0) Contexts under empty transition.

Parameters:

C - the set of LR(0) Contexts whose reflexive transitive closure is computed under empty transition.

Returns:

the reflexive transitive closure of from under empty transition.

expected

Lexicon.Set expected(LR0_Grammar.Contexts C)

Computes the terminals expected in a set of LR(0) Contexts.

Parameters:

C - the set of LR(0) Contexts.

Returns:

the terminals matching a shift or reduce Context in C.

initial

LR0_Grammar.Contexts initial()

Computes the initial state of the LR(0) DFA.

interpret

Object interpret(LineNumberReader source)
           throws Lexicon.Exception

Interprets a source character stream by LR shift-reduce ascent.

Overrides:

interpret in class Grammar

Parameters:

source - the source character stream.

Returns:

the ParseTree constructed by interpreting source.

Throws:

Lexicon.Exception - if an I/O, lexical, syntax or semantic error occurs.

parse

Grammar.Production parse(LR0_Grammar.Contexts C,
                         Object a)

Computes the Production to use in a reverse rightmost derivation.

Parameters:

C - the set of LR(0) Contexts.

a - the lookahead terminal.

Returns:

the highest priority Production underlying an applicable reduce Context in C; returns null if none.

toString

public String toString()

Returns the string representation of this parser, specifically "LR(0)".

Returns:

the string representation of this parser, specifically "LR(0)".

Since:

1.1

transition

LR0_Grammar.Contexts transition(LR0_Grammar.Contexts C,
                                Object X)

Computes a transition from a set of LR(0) Contexts on a symbol.

Parameters:

C - the set of LR(0) Contexts from which the transition is made.

X - the symbol on which the transition is made.

Returns:

the set of LR(0) Contexts to which the transition is made.