/**
* From {@code A|B|..|Z} alternative block build
*
* <pre>
* o->o-A->o->o (last ATNState is BlockEndState pointed to by all alts)
* | ^
* |->o-B->o--|
* | |
* ... |
* | |
* |->o-Z->o--|
* </pre>
*
* So start node points at every alternative with epsilon transition and every alt right side
* points at a block end ATNState.
*
* <p>Special case: only one alternative: don't make a block with alt begin/end.
*
* <p>Special case: if just a list of tokens/chars/sets, then collapse to a single edged o-set->o
* graph.
*
* <p>TODO: Set alt number (1..n) in the states?
*/
@NotNull
@Override
public Handle block(
@NotNull BlockAST blkAST, @NotNull GrammarAST ebnfRoot, @NotNull List<Handle> alts) {
if (ebnfRoot == null) {
if (alts.size() == 1) {
Handle h = alts.get(0);
blkAST.atnState = h.left;
return h;
}
BlockStartState start = newState(BasicBlockStartState.class, blkAST);
if (alts.size() > 1) atn.defineDecisionState(start);
return makeBlock(start, blkAST, alts);
}
switch (ebnfRoot.getType()) {
case ANTLRParser.OPTIONAL:
BlockStartState start = newState(BasicBlockStartState.class, blkAST);
atn.defineDecisionState(start);
Handle h = makeBlock(start, blkAST, alts);
return optional(ebnfRoot, h);
case ANTLRParser.CLOSURE:
BlockStartState star = newState(StarBlockStartState.class, ebnfRoot);
if (alts.size() > 1) atn.defineDecisionState(star);
h = makeBlock(star, blkAST, alts);
return star(ebnfRoot, h);
case ANTLRParser.POSITIVE_CLOSURE:
PlusBlockStartState plus = newState(PlusBlockStartState.class, ebnfRoot);
if (alts.size() > 1) atn.defineDecisionState(plus);
h = makeBlock(plus, blkAST, alts);
return plus(ebnfRoot, h);
}
return null;
}
protected Handle makeBlock(BlockStartState start, BlockAST 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(atn);
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;
}