private Match GetMatch(int state, LabeledTree <TSourceNodeType> self)
{
if (_finals.TryGetValue(state, out RuleBase <TSource, TTarget> rule))
{
var cost = rule.Cost;
foreach (var wildcardBinding in rule.RecurseOnWildcards(self))
{
//
// Basic consistency check below. Making sure the fact the rule led us to bind
// a wildcard originates from indeed having a wildcard label.
//
// Note: To check state table consistency, we could check whether the labeled
// tree (wildcardBinding.Tree.Value.Tree) can be assigned to any of
// the wildcards, using an Any predicate. (For debugging only.)
//
var labels = wildcardBinding.Tree.Value.Labels;
Invariant.Assert(labels.OfType <Match.Wildcard>().Any(), "No assignable wildcard found.");
//
// In case of optimizers we can be faced with partial coverings. The reduction
// phase will make sure we can cover the whole tree if needed.
//
var cheapest = labels.OfType <Match.Final>().OrderBy(final => final.Cost).FirstOrDefault();
if (cheapest != null)
{
cost += cheapest.Cost;
}
}
return(new Match.Final(state, cost));
}
return(new Match(state));
}
private TTarget Reduce(LabeledTree <TSourceNodeType> labeled) => ReduceCore(labeled);
private LabeledTree <TSourceNodeType> LabelCore(ITree <TSourceNodeType> node)
{
var matches = GetWildcardMatches(node).ToList();
var label = new Label <TSourceNodeType>(node, matches);
var res = new LabeledTree <TSourceNodeType>(label, node.Children.Select(childNode => LabelCore(childNode)));
if (res.Children.Count == 0)
{
var sourceNode = (TSource)node;
if (_constants.TryGetValue(sourceNode, out int constantState))
{
matches.Add(GetMatch(constantState, res));
}
foreach (var leafTest in _leafTests)
{
if (leafTest.Key(sourceNode))
{
var leafState = leafTest.Value;
matches.Add(GetMatch(leafState, res));
}
}
}
else
{
// TODO: How should we deal with the concept of "base definitions"?
// What about string.Equals(string) match against string.Equals(object)?
// Contravariance for signatures based on child nodes and a property of the tree node?
if (_states.TryGetValue(node.Value, out NAryMap <int, int> operatorStateMap) && res.Children.Count == operatorStateMap.Levels)
{
var maps = new List <NAryMapOrLeaf <int, int> >
{
NAryMapOrLeaf <int, int> .CreateMap(operatorStateMap)
};
//
// This is the core of the labeling algorithm. We scan the recursively labeled children
// (which correspond to the operator's operands) one-by-one, trying to make progress in
// the state map for the operator by indexing one operand state at a time.
//
// E.g. [1,3] (op) [2,4,7]
//
// Given the state transition map of operator (op), we index into the map using the
// matching states associated with the first operand, i.e. [1,3]. This will give us
// at most two new maps, resembling partial application of (op) with only the first
// operand. Next, we index into those maps using the second child's matching states
// (i.e. [2,4,7]) which gives us the next (and final "leaf") level of maps.
//
foreach (var labeledChild in res.Children)
{
var newMap = new List <NAryMapOrLeaf <int, int> >();
//
// All of the possible states for current child (operand) need to be attempted in the
// current maps. This gives us the next level of maps.
//
var labels = labeledChild.Value.Labels;
foreach (var childLabel in labels)
{
foreach (var map in maps)
{
if (map.Map.TryGetValue(childLabel.State, out NAryMapOrLeaf <int, int> nxt))
{
newMap.Add(nxt);
}
}
}
maps = newMap;
}
foreach (var map in maps)
{
matches.Add(GetMatch(map.Leaf, res));
}
}
}
//
// If a node is assignable to a wildcard but has no available reduction, we can try the
// fallback strategy of local evaluation by funcletizing the remainder tree.
//
if (ShouldConsiderFallback(matches))
{
var sourceNode = (TSource)node;
foreach (var fallbackTest in _fallbackTests)
{
if (fallbackTest.Key(sourceNode))
{
var fallbackState = fallbackTest.Value;
matches.Add(GetMatch(fallbackState, res));
}
}
}
return(res);
}