Package org.antlr.analysis

Class NFAConfiguration

  • public class NFAConfiguration
extends java.lang.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 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

    • Method Summary

      All Methods Instance Methods Concrete Methods 
      Modifier and Type Method Description
      boolean equals​(java.lang.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()  
      java.lang.String toString()  
      java.lang.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

    • Method Detail

      • equals

        public boolean equals​(java.lang.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 java.lang.Object

      • hashCode

        public int hashCode()
        Overrides:
        hashCode in class java.lang.Object

      • toString

        public java.lang.String toString()
        Overrides:
        toString in class java.lang.Object

      • toString

        public java.lang.String toString​(boolean showAlt)