org.antlr.analysis

Class NFAConfiguration

java.lang.Object

org.antlr.analysis.NFAConfiguration

public class NFAConfiguration
extends Object

An NFA state, predicted alt, and syntactic/semantic context. The syntactic context is a pointer into the rule invocation chain used to arrive at the state. The semantic context is the unordered set semantic predicates encountered before reaching an NFA state.

Field Summary

Fields

Modifier and Type	Field and Description
int	alt What alt is predicted by this configuration
NFAContext	context What is the stack of rule invocations that got us to state?
protected int	numberEpsilonTransitionsEmanatingFromState Lots of NFA states have only epsilon edges (1 or 2).
protected boolean	resolved Indicate that this configuration has been resolved and no further DFA processing should occur with it.
protected boolean	resolveWithPredicate This bit is used to indicate a semantic predicate will be used to resolve the conflict.
SemanticContext	semanticContext The set of semantic predicates associated with this NFA configuration.
protected boolean	singleAtomTransitionEmanating Indicates that the NFA state associated with this configuration has exactly one transition and it's an atom (not epsilon etc...).
int	state The NFA state associated with this configuration

Constructor Summary

Constructors

Constructor and Description
NFAConfiguration(int state, int alt, NFAContext context, SemanticContext semanticContext)

Method Summary

Methods

Modifier and Type	Method and Description
boolean	equals(Object o) An NFA configuration is equal to another if both have the same state, the predict the same alternative, and syntactic/semantic contexts are the same.
int	hashCode()
String	toString()
String	toString(boolean showAlt)

Methods inherited from class java.lang.Object

clone, finalize, getClass, notify, notifyAll, wait, wait, wait

Field Detail

state

public int state

The NFA state associated with this configuration

alt

public int alt

What alt is predicted by this configuration

context

public NFAContext context

What is the stack of rule invocations that got us to state?

semanticContext

public SemanticContext semanticContext

The set of semantic predicates associated with this NFA configuration. The predicates were found on the way to the associated NFA state in this syntactic context. Set<AST>: track nodes in grammar containing the predicate for error messages and such (nice to know where the predicate came from in case of duplicates etc...). By using a set, the equals() method will correctly show {pred1,pred2} as equals() to {pred2,pred1}.

resolved

protected boolean resolved

Indicate that this configuration has been resolved and no further DFA processing should occur with it. Essentially, this is used as an "ignore" bit so that upon a set of nondeterministic configurations such as (s|2) and (s|3), I can set (s|3) to resolved=true (and any other configuration associated with alt 3).

resolveWithPredicate

protected boolean resolveWithPredicate

This bit is used to indicate a semantic predicate will be used to resolve the conflict. Method DFA.findNewDFAStatesAndAddDFATransitions will add edges for the predicates after it performs the reach operation. The nondeterminism resolver sets this when it finds a set of nondeterministic configurations (as it does for "resolved" field) that have enough predicates to resolve the conflit.

numberEpsilonTransitionsEmanatingFromState

protected int numberEpsilonTransitionsEmanatingFromState

Lots of NFA states have only epsilon edges (1 or 2). We can safely consider only n>0 during closure.

singleAtomTransitionEmanating

protected boolean singleAtomTransitionEmanating

Indicates that the NFA state associated with this configuration has exactly one transition and it's an atom (not epsilon etc...).

Constructor Detail

NFAConfiguration

public NFAConfiguration(int state,
                int alt,
                NFAContext context,
                SemanticContext semanticContext)

Method Detail

equals

public boolean equals(Object o)

An NFA configuration is equal to another if both have the same state, the predict the same alternative, and syntactic/semantic contexts are the same. I don't think the state|alt|ctx could be the same and have two different semantic contexts, but might as well define equals to be everything.

Overrides:

equals in class Object

hashCode

public int hashCode()

Overrides:

hashCode in class Object

toString

public String toString()

Overrides:

toString in class Object

toString

public String toString(boolean showAlt)