antlr-3.4/tool/src/main/java/org/antlr/analysis/NFAConfiguration.java

/*
 * [The "BSD license"]
 *  Copyright (c) 2010 Terence Parr
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package org.antlr.analysis;

import org.antlr.misc.Utils;

/** 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.
 */
public class NFAConfiguration {
    /** The NFA state associated with this configuration */
    public int state;

    /** What alt is predicted by this configuration */
    public int alt;

    /** What is the stack of rule invocations that got us to state? */
    public NFAContext context;

    /** 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}.
     */
    public SemanticContext semanticContext = SemanticContext.EMPTY_SEMANTIC_CONTEXT;

    /** 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).
     */
    protected boolean resolved;

    /** 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.
     */
    protected boolean resolveWithPredicate;

    /** Lots of NFA states have only epsilon edges (1 or 2).  We can
     *  safely consider only n>0 during closure.
     */
    protected int numberEpsilonTransitionsEmanatingFromState;

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

	//protected boolean addedDuringClosure = true;

	public NFAConfiguration(int state,
                            int alt,
                            NFAContext context,
                            SemanticContext semanticContext)
    {
        this.state = state;
        this.alt = alt;
        this.context = context;
        this.semanticContext = semanticContext;
    }

    /** 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.
     */
    public boolean equals(Object o) {
		if ( o==null ) {
			return false;
		}
        NFAConfiguration other = (NFAConfiguration)o;
        return this.state==other.state &&
               this.alt==other.alt &&
               this.context.equals(other.context)&&
               this.semanticContext.equals(other.semanticContext);
    }

    public int hashCode() {
        int h = state + alt + context.hashCode();
        return h;
    }

	public String toString() {
		return toString(true);
	}

	public String toString(boolean showAlt) {
		StringBuffer buf = new StringBuffer();
		buf.append(state);
		if ( showAlt ) {
			buf.append("|");
			buf.append(alt);
		}
		if ( context.parent!=null ) {
            buf.append("|");
            buf.append(context);
        }
        if ( semanticContext!=null &&
             semanticContext!=SemanticContext.EMPTY_SEMANTIC_CONTEXT ) {
            buf.append("|");
			String escQuote = Utils.replace(semanticContext.toString(), "\"", "\\\"");
			buf.append(escQuote);
        }
        if ( resolved ) {
            buf.append("|resolved");
        }
		if ( resolveWithPredicate ) {
			buf.append("|resolveWithPredicate");
		}
		return buf.toString();
    }
}