Package org.antlr.analysis

Class NFAState

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

    • Field Detail

      • 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 java.lang.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 Detail

      • NFAState

        public NFAState​(NFA nfa)

    • Method Detail

      • setTransition0

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

      • 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 java.lang.String getDescription()

      • setDescription

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