/// <summary>
/// Ask the knowledge base if a given statement about the model is true, given what it knows.
/// </summary>
/// <param name="query"></param>
/// <returns>True if the statement is known to be true, false if it is known to be false or cannot be determined.</returns>
public bool Ask(Expression <Predicate <TModel> > query)
{
// NB: Very raw implementation - there are a number of possible performance improvements that could be made here
// Will return to give them a go at some point..
var queryAsCnf = new CNFExpression <TModel>(query);
var clauses = sentences.Append(queryAsCnf).SelectMany(s => s.Clauses).ToList();
List <CNFClause <TModel> > newClauses = new List <CNFClause <TModel> >();
while (true)
{
// TODO-PERFORMANCE: While this is how the source book writes the algorithm, its very inefficient -
// we'll end up resolving the same clauses again and again. Need to improve this (and move this
// implementation to the benchmarks project as a baseline).
foreach (var ci in clauses)
{
foreach (var cj in clauses)
{
var resolvents = CNFClause <TModel> .Resolve(ci, cj);
if (resolvents.IsEmpty)
{
return(true);
}
newClauses.Add(resolvents);
}
}
// if new ⊆ clauses then return false // need clause equality..
clauses.AddRange(newClauses);
}
return(false);
}
public void TestCNFClause()
{
CNFClause clause1 = new CNFClause(ClauseParser.Parse("a&b&c||d")),
clause2 = new CNFClause(ClauseParser.Parse("a=>(b&c||d&e)"));
Console.WriteLine("{0}\n{1}", clause1.ToString(), clause2.ToString());
}
