public static void FindKnownStates(Tree tree, ICollection <string> knownStates)
{
if (tree.IsLeaf() || tree.IsPreTerminal())
{
return;
}
if (!ShiftReduceUtils.IsTemporary(tree))
{
knownStates.Add(tree.Value());
}
foreach (Tree child in tree.Children())
{
FindKnownStates(child, knownStates);
}
}
/// <summary>Legal as long as there are at least two items on the state's stack.</summary>
public virtual bool IsLegal(State state, IList <ParserConstraint> constraints)
{
// some of these quotes come directly from Zhang Clark 09
if (state.finished)
{
return(false);
}
if (state.stack.Size() <= 1)
{
return(false);
}
// at least one of the two nodes on top of stack must be non-temporary
if (ShiftReduceUtils.IsTemporary(state.stack.Peek()) && ShiftReduceUtils.IsTemporary(state.stack.Pop().Peek()))
{
return(false);
}
if (ShiftReduceUtils.IsTemporary(state.stack.Peek()))
{
if (side == BinaryTransition.Side.Left)
{
return(false);
}
if (!ShiftReduceUtils.IsEquivalentCategory(label, state.stack.Peek().Value()))
{
return(false);
}
}
if (ShiftReduceUtils.IsTemporary(state.stack.Pop().Peek()))
{
if (side == BinaryTransition.Side.Right)
{
return(false);
}
if (!ShiftReduceUtils.IsEquivalentCategory(label, state.stack.Pop().Peek().Value()))
{
return(false);
}
}
// don't allow binarized labels if it makes the state have a stack
// of size 1 and a queue of size 0
if (state.stack.Size() == 2 && IsBinarized() && state.EndOfQueue())
{
return(false);
}
// when the stack contains only two nodes, temporary resulting
// nodes from binary reduce must be left-headed
if (state.stack.Size() == 2 && IsBinarized() && side == BinaryTransition.Side.Right)
{
return(false);
}
// when the queue is empty and the stack contains more than two
// nodes, with the third node from the top being temporary, binary
// reduce can be applied only if the resulting node is non-temporary
if (state.EndOfQueue() && state.stack.Size() > 2 && ShiftReduceUtils.IsTemporary(state.stack.Pop().Pop().Peek()) && IsBinarized())
{
return(false);
}
// when the stack contains more than two nodes, with the third
// node from the top being temporary, temporary resulting nodes
// from binary reduce must be left-headed
if (state.stack.Size() > 2 && ShiftReduceUtils.IsTemporary(state.stack.Pop().Pop().Peek()) && IsBinarized() && side == BinaryTransition.Side.Right)
{
return(false);
}
if (constraints == null)
{
return(true);
}
Tree top = state.stack.Peek();
int leftTop = ShiftReduceUtils.LeftIndex(top);
int rightTop = ShiftReduceUtils.RightIndex(top);
Tree next = state.stack.Pop().Peek();
int leftNext = ShiftReduceUtils.LeftIndex(next);
// The binary transitions are affected by constraints in the
// following two circumstances. If a transition would cross the
// left boundary of a constraint, that is illegal. If the
// transition is exactly the right size for the constraint and
// would make a temporary node, that is also illegal.
foreach (ParserConstraint constraint in constraints)
{
if (leftTop == constraint.start)
{
// can't binary reduce away from a tree which doesn't match a constraint
if (rightTop == constraint.end - 1)
{
if (!ShiftReduceUtils.ConstraintMatchesTreeTop(top, constraint))
{
return(false);
}
else
{
continue;
}
}
else
{
if (rightTop >= constraint.end)
{
continue;
}
else
{
// can't binary reduce if it would make the tree cross the left boundary
return(false);
}
}
}
// top element is further left than the constraint, so
// there's no harm to be done by binary reduce
if (leftTop < constraint.start)
{
continue;
}
// top element is past the end of the constraint, so it must already be satisfied
if (leftTop >= constraint.end)
{
continue;
}
// now leftTop > constraint.start and < constraint.end, eg inside the constraint
// the next case is no good because it crosses the boundary
if (leftNext < constraint.start)
{
return(false);
}
if (leftNext > constraint.start)
{
continue;
}
// can't transition to a binarized node when there's a constraint that matches.
if (rightTop == constraint.end - 1 && IsBinarized())
{
return(false);
}
}
return(true);
}
/// <summary>
/// Returns a transition which might not even be part of the model,
/// but will hopefully allow progress in an otherwise stuck parse
/// TODO: perhaps we want to create an EmergencyTransition class
/// which indicates that something has gone wrong
/// </summary>
public virtual ITransition FindEmergencyTransition(State state, IList <ParserConstraint> constraints)
{
if (state.stack.Size() == 0)
{
return(null);
}
// See if there is a constraint whose boundaries match the end
// points of the top node on the stack. If so, we can apply a
// UnaryTransition / CompoundUnaryTransition if that would solve
// the constraint
if (constraints != null)
{
Tree top = state.stack.Peek();
foreach (ParserConstraint constraint in constraints)
{
if (ShiftReduceUtils.LeftIndex(top) != constraint.start || ShiftReduceUtils.RightIndex(top) != constraint.end - 1)
{
continue;
}
if (ShiftReduceUtils.ConstraintMatchesTreeTop(top, constraint))
{
continue;
}
// found an unmatched constraint that can be fixed with a unary transition
// now we need to find a matching state for the transition
foreach (string label in knownStates)
{
if (constraint.state.Matcher(label).Matches())
{
return((op.compoundUnaries) ? new CompoundUnaryTransition(Java.Util.Collections.SingletonList(label), false) : new UnaryTransition(label, false));
}
}
}
}
if (ShiftReduceUtils.IsTemporary(state.stack.Peek()) && (state.stack.Size() == 1 || ShiftReduceUtils.IsTemporary(state.stack.Pop().Peek())))
{
return((op.compoundUnaries) ? new CompoundUnaryTransition(Java.Util.Collections.SingletonList(Sharpen.Runtime.Substring(state.stack.Peek().Value(), 1)), false) : new UnaryTransition(Sharpen.Runtime.Substring(state.stack.Peek().Value(), 1),
false));
}
if (state.stack.Size() == 1 && state.tokenPosition >= state.sentence.Count)
{
// either need to finalize or transition to a root state
if (!rootStates.Contains(state.stack.Peek().Value()))
{
string root = rootStates.GetEnumerator().Current;
return((op.compoundUnaries) ? new CompoundUnaryTransition(Java.Util.Collections.SingletonList(root), false) : new UnaryTransition(root, false));
}
}
if (state.stack.Size() == 1)
{
return(null);
}
if (ShiftReduceUtils.IsTemporary(state.stack.Peek()))
{
return(new BinaryTransition(Sharpen.Runtime.Substring(state.stack.Peek().Value(), 1), BinaryTransition.Side.Right));
}
if (ShiftReduceUtils.IsTemporary(state.stack.Pop().Peek()))
{
return(new BinaryTransition(Sharpen.Runtime.Substring(state.stack.Pop().Peek().Value(), 1), BinaryTransition.Side.Left));
}
return(null);
}
