Class NFAState

java.lang.Object
org.antlr.analysis.State
org.antlr.analysis.NFAState

public class NFAState extends State
A state within an NFA. At most 2 transitions emanate from any NFA state.
  • Field Details

    • LOOPBACK

      public static final int LOOPBACK
      See Also:
    • BLOCK_START

      public static final int BLOCK_START
      See Also:
    • OPTIONAL_BLOCK_START

      public static final int OPTIONAL_BLOCK_START
      See Also:
    • BYPASS

      public static final int BYPASS
      See Also:
    • RIGHT_EDGE_OF_BLOCK

      public static final int RIGHT_EDGE_OF_BLOCK
      See Also:
    • MAX_TRANSITIONS

      public static final int MAX_TRANSITIONS
      See Also:
    • numTransitions

      int numTransitions
      How many transitions; 0, 1, or 2 transitions
    • transition

      public Transition[] transition
    • incidentEdgeLabel

      public Label incidentEdgeLabel
      For o-A->o type NFA tranitions, record the label that leads to this state. Useful for creating rich error messages when we find insufficiently (with preds) covered states.
    • nfa

      public NFA nfa
      Which NFA are we in?
    • decisionNumber

      protected int decisionNumber
      What's its decision number from 1..n?
    • decisionStateType

      public int decisionStateType
      Subrules (...)* and (...)+ have more than one decision point in the NFA created for them. They both have a loop-exit-or-stay-in decision node (the loop back node). They both have a normal alternative block decision node at the left edge. The (...)* is worse as it even has a bypass decision (2 alts: stay in or bypass) node at the extreme left edge. This is not how they get generated in code as a while-loop or whatever deals nicely with either. For error messages (where I need to print the nondeterministic alts) and for interpretation, I need to use the single DFA that is created (for efficiency) but interpret the results differently depending on which of the 2 or 3 decision states uses the DFA. For example, the DFA will always report alt n+1 as the exit branch for n real alts, so I need to translate that depending on the decision state. If decisionNumber>0 then this var tells you what kind of decision state it is.
    • enclosingRule

      public Rule enclosingRule
      What rule do we live in?
    • description

      protected String description
      During debugging and for nondeterminism warnings, it's useful to know what relationship this node has to the original grammar. For example, "start of alt 1 of rule a".
    • associatedASTNode

      public GrammarAST associatedASTNode
      Associate this NFAState with the corresponding GrammarAST node from which this node was created. This is useful not only for associating the eventual lookahead DFA with the associated Grammar position, but also for providing users with nondeterminism warnings. Mainly used by decision states to report line:col info. Could also be used to track line:col for elements such as token refs.
    • EOTTargetState

      protected boolean EOTTargetState
      Is this state the sole target of an EOT transition?
    • endOfBlockStateNumber

      public int endOfBlockStateNumber
      Jean Bovet needs in the GUI to know which state pairs correspond to the start/stop of a block.
  • Constructor Details

    • NFAState

      public NFAState(NFA nfa)
  • Method Details

    • getNumberOfTransitions

      public int getNumberOfTransitions()
      Specified by:
      getNumberOfTransitions in class State
    • addTransition

      public void addTransition(Transition e)
      Specified by:
      addTransition in class State
    • setTransition0

      public void setTransition0(Transition e)
      Used during optimization to reset a state to have the (single) transition another state has.
    • transition

      public Transition transition(int i)
      Specified by:
      transition in class State
    • translateDisplayAltToWalkAlt

      public int translateDisplayAltToWalkAlt(int displayAlt)
      The DFA decision for this NFA decision state always has an exit path for loops as n+1 for n alts in the loop. That is really useful for displaying nondeterministic alts and so on, but for walking the NFA to get a sequence of edge labels or for actually parsing, we need to get the real alt number. The real alt number for exiting a loop is always 1 as transition 0 points at the exit branch (we compute DFAs always for loops at the loopback state). For walking/parsing the loopback state: 1 2 3 display alt (for human consumption) 2 3 1 walk alt For walking the block start: 1 2 3 display alt 1 2 3 For walking the bypass state of a (...)* loop: 1 2 3 display alt 1 1 2 all block alts map to entering loop exit means take bypass Non loop EBNF do not need to be translated; they are ignored by this method as decisionStateType==0. Return same alt if we can't translate.
    • setDecisionASTNode

      public void setDecisionASTNode(GrammarAST decisionASTNode)
      What AST node is associated with this NFAState? When you set the AST node, I set the node to point back to this NFA state.
    • getDescription

      public String getDescription()
    • setDescription

      public void setDescription(String description)
    • getDecisionNumber

      public int getDecisionNumber()
    • setDecisionNumber

      public void setDecisionNumber(int decisionNumber)
    • isEOTTargetState

      public boolean isEOTTargetState()
    • setEOTTargetState

      public void setEOTTargetState(boolean eot)
    • isDecisionState

      public boolean isDecisionState()
    • toString

      public String toString()
      Overrides:
      toString in class Object