/**
* From {@code (A)?} build either:
*
* <pre>
* o--A->o
* | ^
* o---->|
* </pre>
*
* or, if {@code A} is a block, just add an empty alt to the end of the block
*/
@Override
public Handle optional(GrammarAST optAST, Handle blk) {
BlockStartState blkStart = (BlockStartState) blk.left;
ATNState blkEnd = blk.right;
preventEpsilonOptionalBlocks.add(
new Triple<Rule, ATNState, ATNState>(currentRule, blkStart, blkEnd));
boolean greedy = ((QuantifierAST) optAST).isGreedy();
blkStart.nonGreedy = !greedy;
epsilon(blkStart, blk.right, !greedy);
optAST.atnState = blk.left;
return blk;
}
protected Handle makeBlock(BlockStartState start, GrammarAST blkAST, List<Handle> alts) {
BlockEndState end = newState(BlockEndState.class, blkAST);
start.endState = end;
for (Handle alt : alts) {
// hook alts up to decision block
epsilon(start, alt.left);
epsilon(alt.right, end);
// no back link in ATN so must walk entire alt to see if we can
// strip out the epsilon to 'end' state
TailEpsilonRemover opt = new TailEpsilonRemover();
opt.visit(alt.left);
}
Handle h = new Handle(start, end);
// FASerializer ser = new FASerializer(g, h.left);
// System.out.println(blkAST.toStringTree()+":\n"+ser);
blkAST.atnState = start;
return h;
}