/**
* From (blk)* build ( blk+ )? with *two* decisions, one for entry and one for choosing alts of
* blk.
*
* <p>|-------------| v | o--[o-blk-o]->o o | ^ -----------------|
*
* <p>Note that the optional bypass must jump outside the loop as (A|B)* is not the same thing as
* (A|B|)+.
*/
@NotNull
public Handle star(@NotNull GrammarAST starAST, @NotNull Handle elem) {
StarBlockStartState blkStart = (StarBlockStartState) elem.left;
BlockEndState blkEnd = (BlockEndState) elem.right;
StarLoopEntryState entry = newState(StarLoopEntryState.class, starAST);
atn.defineDecisionState(entry);
LoopEndState end = newState(LoopEndState.class, starAST);
StarLoopbackState loop = newState(StarLoopbackState.class, starAST);
entry.loopBackState = loop;
end.loopBackStateNumber = loop.stateNumber;
BlockAST blkAST = (BlockAST) starAST.getChild(0);
entry.isGreedy = isGreedy(blkAST);
if (!g.isLexer() || entry.isGreedy) {
epsilon(entry, blkStart); // loop enter edge (alt 1)
epsilon(entry, end); // bypass loop edge (alt 2)
} else { // only lexers flip entry/exit branches for nongreedy
// if not greedy, priority to exit branch; make it first
epsilon(entry, end); // bypass loop edge (alt 1)
epsilon(entry, blkStart); // loop enter edge (alt 2)
}
epsilon(blkEnd, loop); // block end hits loop back
epsilon(loop, entry); // loop back to entry/exit decision
starAST.atnState = entry; // decision is to enter/exit; blk is its own decision
return new Handle(entry, end);
}
/**
* From (blk)+ build
*
* <p>|---------| v | [o-blk-o]->o->o
*
* <p>We add a decision for loop back node to the existing one at blk start.
*/
@NotNull
public Handle plus(@NotNull GrammarAST plusAST, @NotNull Handle blk) {
PlusBlockStartState blkStart = (PlusBlockStartState) blk.left;
BlockEndState blkEnd = (BlockEndState) blk.right;
PlusLoopbackState loop = newState(PlusLoopbackState.class, plusAST);
atn.defineDecisionState(loop);
LoopEndState end = newState(LoopEndState.class, plusAST);
blkStart.loopBackState = loop;
end.loopBackStateNumber = loop.stateNumber;
plusAST.atnState = blkStart;
epsilon(blkEnd, loop); // blk can see loop back
BlockAST blkAST = (BlockAST) plusAST.getChild(0);
loop.isGreedy = isGreedy(blkAST);
if (!g.isLexer() || loop.isGreedy) {
epsilon(loop, blkStart); // loop back to start
epsilon(loop, end); // or exit
} else { // only lexers flip entry/exit branches for nongreedy
// if not greedy, priority to exit branch; make it first
epsilon(loop, end); // exit
epsilon(loop, blkStart); // loop back to start
}
return new Handle(blkStart, end);
}