org.antlr.analysis

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 Summary

Fields

Modifier and Type	Field and Description
GrammarAST	associatedASTNode Associate this NFAState with the corresponding GrammarAST node from which this node was created.
static int	BLOCK_START
static int	BYPASS
protected int	decisionNumber What's its decision number from 1..n?
int	decisionStateType Subrules (...)* and (...)+ have more than one decision point in the NFA created for them.
protected String	description During debugging and for nondeterminism warnings, it's useful to know what relationship this node has to the original grammar.
Rule	enclosingRule What rule do we live in?
int	endOfBlockStateNumber Jean Bovet needs in the GUI to know which state pairs correspond to the start/stop of a block.
protected boolean	EOTTargetState Is this state the sole target of an EOT transition?
Label	incidentEdgeLabel For o-A->o type NFA tranitions, record the label that leads to this state.
static int	LOOPBACK
static int	MAX_TRANSITIONS
NFA	nfa Which NFA are we in?
static int	OPTIONAL_BLOCK_START
static int	RIGHT_EDGE_OF_BLOCK
Transition[]	transition

Fields inherited from class org.antlr.analysis.State

acceptState, INVALID_STATE_NUMBER, stateNumber

Constructor Summary

Constructors

Constructor and Description
NFAState(NFA nfa)

Method Summary

Methods

Modifier and Type	Method and Description
void	addTransition(Transition e)
int	getDecisionNumber()
String	getDescription()
int	getNumberOfTransitions()
boolean	isDecisionState()
boolean	isEOTTargetState()
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.
void	setDecisionNumber(int decisionNumber)
void	setDescription(String description)
void	setEOTTargetState(boolean eot)
void	setTransition0(Transition e) Used during optimization to reset a state to have the (single) transition another state has.
String	toString()
Transition	transition(int i)
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.

Methods inherited from class org.antlr.analysis.State

isAcceptState, setAcceptState

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, wait

Field Detail

LOOPBACK

public static final int LOOPBACK

See Also:

Constant Field Values

BLOCK_START

public static final int BLOCK_START

See Also:

Constant Field Values

OPTIONAL_BLOCK_START

public static final int OPTIONAL_BLOCK_START

See Also:

Constant Field Values

BYPASS

public static final int BYPASS

See Also:

Constant Field Values

RIGHT_EDGE_OF_BLOCK

public static final int RIGHT_EDGE_OF_BLOCK

See Also:

Constant Field Values

MAX_TRANSITIONS

public static final int MAX_TRANSITIONS

See Also:

Constant Field Values

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 Detail

NFAState

public NFAState(NFA nfa)

Method Detail

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