java.lang.Objectantlr.Lookahead
This object holds all information needed to represent the lookahead for any particular lookahead computation for a single lookahead depth. Final lookahead information is a simple bit set, but intermediate stages need computation cycle and FOLLOW information.
Concerning the cycle variable. If lookahead is computed for a RuleEnd node, then computation is part of a FOLLOW cycle for this rule. If lookahead is computed for a RuleBlock node, the computation is part of a FIRST cycle to this rule.
Concerning the epsilonDepth variable. This is not the depth relative to the rule reference that epsilon was encountered. That value is
initial_k - epsilonDepth + 1Also, lookahead depths past rule ref for local follow are:
initial_k - (initial_k - epsilonDepth)Used for rule references. If we try to compute look(k, ruleref) and there are fewer than k lookahead terminals before the end of the the rule, epsilon will be returned (don't want to pass the end of the rule). We must track when the the lookahead got stuck. For example,
a : b A B E F G; b : C ;LOOK(5, ref-to(b)) is {
a : b A B C ; b : E F // epsilon depth of 1 relative to initial k=3 | G // epsilon depth of 2 ;Here, LOOK(3,ref-to(b)) returns epsilon, but the depths are {1, 2}; i.e., 3-(3-1) and 3-(3-2). Those are the lookahead depths past the rule ref needed for the local follow.
This is null unless an epsilon is created.
combineWith(Lookahead)
Constructor Summary | |
Lookahead()
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Lookahead(BitSet p)
create a new lookahead set with the LL(1) set to the parameter |
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Lookahead(java.lang.String c)
create an empty lookahead set, but with cycle |
Method Summary | |
java.lang.Object |
clone()
Make a deep copy of everything in this object |
void |
combineWith(Lookahead q)
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boolean |
containsEpsilon()
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Lookahead |
intersection(Lookahead q)
What is the intersection of two lookahead depths? Only the Epsilon "bit" and bitset are considered. |
boolean |
nil()
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static Lookahead |
of(int el)
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void |
resetEpsilon()
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void |
setEpsilon()
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java.lang.String |
toString()
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java.lang.String |
toString(java.lang.String separator,
CharFormatter formatter)
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java.lang.String |
toString(java.lang.String separator,
CharFormatter formatter,
Grammar g)
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java.lang.String |
toString(java.lang.String separator,
Vector vocab)
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Methods inherited from class java.lang.Object |
equals, getClass, hashCode, notify, notifyAll, wait, wait, wait |
Constructor Detail |
public Lookahead()
public Lookahead(BitSet p)
public Lookahead(java.lang.String c)
Method Detail |
public java.lang.Object clone()
public void combineWith(Lookahead q)
public boolean containsEpsilon()
public Lookahead intersection(Lookahead q)
public boolean nil()
public static Lookahead of(int el)
public void resetEpsilon()
public void setEpsilon()
public java.lang.String toString()
public java.lang.String toString(java.lang.String separator, CharFormatter formatter)
public java.lang.String toString(java.lang.String separator, CharFormatter formatter, Grammar g)
public java.lang.String toString(java.lang.String separator, Vector vocab)