antlr
public class Lookahead extends Object implements Cloneable
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.
See Also: combineWith
Field Summary | |
---|---|
String | cycle is this computation part of a computation cycle? |
BitSet | epsilonDepth What k values were being computed when end of rule hit? |
BitSet | fset actual bitset of the lookahead |
boolean | hasEpsilon Does this lookahead depth include Epsilon token type? |
Constructor Summary | |
---|---|
Lookahead() | |
Lookahead(BitSet p) create a new lookahead set with the LL(1) set to the parameter | |
Lookahead(String c) create an empty lookahead set, but with cycle |
Method Summary | |
---|---|
Object | clone() Make a deep copy of everything in this object |
void | combineWith(Lookahead q) |
boolean | containsEpsilon() |
Lookahead | intersection(Lookahead q) What is the intersection of two lookahead depths?
|
boolean | nil() |
static Lookahead | of(int el) |
void | resetEpsilon() |
void | setEpsilon() |
String | toString() |
String | toString(String separator, CharFormatter formatter) |
String | toString(String separator, CharFormatter formatter, Grammar g) |
String | toString(String separator, Vector vocab) |