private void Predict(Column col, List<Rule> ruleList, State state, NonTerminalObject currObject)
{
if (generator)
{
var rule = Grammar.GetRandomRuleForAGivenLHS(currObject.NonTerminal, true);
ruleList = new List<Rule> {rule};
}
foreach (var rule in ruleList)
{
//TODO: change later to skip -all- rules whose derivation leads to the empty string.
//I.e, A-> B.C , C -> D E. D -> epsilon, E -> epsilon. C itself is not an epsilon rule.
if (rule.IsEpsilonRule() && Grammar.nullableProductions.ContainsKey(currObject))
{
//states that are the result of a spontenous dot shift (due to nullable production)
//have already been added to the agendas in Column.Add()
continue;
}
//if current stack is empty but predicted stack is not, mismatch - do not predict this rule.
if (currObject.IsStackEmpty() && !rule.IsInitialOrDotStack()) continue;
//prepare new rule based on the stack information contained in the current state
//and based on the predicted rule.
var createdRule = new Rule(rule);
//if the rule is not a stack manipulating rule,
if (rule.IsInitialRule())
{
var complementPositionObject = createdRule.Production[createdRule.ComplementPosition];
//if current stack is not empty, but the complement position does not allow for stacks (POS),
//mismatch - do not predict this rule.
if (!currObject.IsStackEmpty() && Grammar.IsPOS(complementPositionObject.NonTerminal)) continue;
//the stack of the LHS of the created rule is the stack of the current object:
createdRule.Name = currObject;
//copy the stack to the complement position.
complementPositionObject.Stack = currObject.Stack;
}
else
{
if (createdRule.Name.Stack.Peek() != "." && currObject.Stack.Top != Grammar.Epsilon &&
currObject.Stack.Top != createdRule.Name.Stack.Peek())
continue;
//if tops of the stacks do not match, continue. e.g created rule PP[PP] -> epsilon, current object: PP[NP].
//create left hand side of new rule.
createdRule.Name.Stack = currObject.Stack;
createdRule.Name.NonTerminal = currObject.NonTerminal;
//create right hand side of new rule.
NonTerminalStack contentOfDot;
if (rule.Name.Stack.Peek() == ".")
contentOfDot = currObject.Stack; //e.g. A[..]
else
contentOfDot = currObject.Stack.GetPrefixListStackObjectOfGivenTop(rule.Name.Stack.Peek());
//e.g A[..X]
for (var i = 0; i < rule.Production.Length; i++)
{
var s = rule.Production[i].Stack;
if (s != null)
{
if (s.Peek() == ".")
createdRule.Production[i].Stack = contentOfDot; // e.g, A[..] pop rule.
else if (s.PrefixList == null)
createdRule.Production[i].Stack = s; //e.g. A[X] //secondary constituent.
else
createdRule.Production[i].Stack = new NonTerminalStack(s.Peek(), contentOfDot);
//e.g. A[..X] - push rule.
//calculate the new weight of the top of the stack from the weights of its sons.
//if (createdRule.Production[i].Stack != null)
// createdRule.Production[i].Stack.Weight = createdRule.Production[i].Stack.PrefixList != null ? createdRule.Production[i].Stack.PrefixList.Sum(x => x.Weight) : 1;
}
}
}
var newState = new State(createdRule, 0, col, null) {LogProbability = ruleLogProbabilities[rule.Number]};
if (newState.LogProbability < 0)
throw new Exception("wrong probability");
var added = col.AddState(newState, ParsingOperation.Predict);
if (Debug)
Console.WriteLine("{0} & {1} & {2} & Predicted from State {3}, added: {4}\\\\", newState.StateNumber,
newState,
col.Index, state.StateNumber, added);
}
}
public Node ParseSentence(string text)
{
string[] arr;
if (text == null)
{
generator = true;
arr = Enumerable.Repeat("", 100).ToArray();
}
else
arr = text.Split();
//check below that the text appears in the vocabulary
if (!generator && arr.Any(str => !Grammar.Vocabulary.ContainsWord(str)))
throw new Exception("word in text does not appear in the vocabulary.");
var table = new Column[arr.Length + 1];
for (var i = 1; i < table.Length; i++)
table[i] = new Column(i, arr[i - 1], Grammar);
table[0] = new Column(0, "", Grammar);
State.stateCounter = 0;
var startRule = new Rule(0, GammaRule, new[] {Grammar.StartSymbol}, 0, 0);
//startRule.Production[0].Stack = new NonTerminalStack(Grammar.EPSILON);
var startState = new State(startRule, 0, table[0], null);
startState.LogProbability = 0.0f;
Node.grammar = Grammar;
table[0].AddState(startState, ParsingOperation.Scan);
var finalColumn = table[table.Length - 1];
try
{
foreach (var col in table)
{
var count = 0;
if (generator && !col.States.Any())
{
finalColumn = table[col.Index - 1];
break;
}
//1. complete
while (col.ActionableCompleteStates.Any())
{
count++;
TestForTooManyStatesInColumn(count, Debug);
var states = col.ActionableCompleteStates.First().Value;
var state = states.Dequeue();
if (!states.Any())
col.ActionableCompleteStates.Remove(state);
if (generator)
state.LogProbability = 0;
Complete(col, state);
}
//2. predict after complete:
while (col.ActionableNonCompleteStates.Any())
{
if (col.ActionableCompleteStates.Any())
throw new Exception(
"completed states queue should always be empty while processing predicted states.");
count++;
TestForTooManyStatesInColumn(count, Debug);
var state = col.ActionableNonCompleteStates.Dequeue();
if (generator)
state.LogProbability = 0;
var currObject = state.NextProductionTerm();
var term = currObject.NonTerminal;
var ruleList = Grammar[term];
if (ruleList != null)
Predict(col, ruleList, state, currObject);
}
//3. scan after predict.
foreach (var state in col)
{
if (!state.IsCompleted())
{
var currObject = state.NextProductionTerm();
var term = currObject.NonTerminal;
if (!generator)
{
if (col.Index + 1 < table.Length &&
Grammar.Vocabulary[table[col.Index + 1].Token].Contains(term))
Scan(table[col.Index + 1], state, term, table[col.Index + 1].Token);
}
else
{
if (Grammar.Vocabulary.POSWithPossibleWords.ContainsKey(term))
{
var ruleList = Grammar[term];
//if the term is a constituent, generate it given some probability. otherwise continue.
if (ruleList != null)
{
if (rand.NextDouble() > ChanceToGenerateConstituent) continue;
if (ruleList[0].IsEpsilonRule())
continue;
//if we generated a predicted epsilon rule for that constituent, don't scan.
}
//selecting random word from vocabulary: (uncomment the next line)
//var index = rand.Next(Vocabulary.POSWithPossibleWords[currentNode.Name].Count);
//always selecting the same word from vocabulary is considerably faster because I do not re-parse the same sentence
//but keep the counts of appearances of the sentence.
//the parse of two sentences with identical sequence of POS is the same - regardless of the actual word selected.
if (table[col.Index + 1].Token == "")
//if the token was already written by a previous scan
//(for instance NP -> John, NP -> D N, D -> the, "John" was already written before "the")
{
var index = 0;
table[col.Index + 1].Token =
Grammar.Vocabulary.POSWithPossibleWords[term].ElementAt(index);
Scan(table[col.Index + 1], state, term, table[col.Index + 1].Token);
}
}
}
}
}
}
foreach (var state in finalColumn.GammaStates)
return state.Node.Children[0];
}
catch (LogException e)
{
var s = e.ToString();
Console.WriteLine(s);
Console.WriteLine(string.Format("sentence: {0}, grammar: {1}", text, Grammar));
}
catch (Exception e)
{
var s = e.ToString();
Console.WriteLine(s);
}
if (!generator)
throw new Exception("Parsing Failed!");
throw new Exception("Generating Failed!");
}
private void Scan(Column col, State state, string term, string token)
{
//if there is nonempty stack arriving to this part of speech term, stop here - the derivation is wrong.
//SEFI - note: this is a restriction on the form of your grammar.
//consider removing it to see the conequences.
//if (Grammar.isPOS(term))
{
if (!state.NextProductionTerm().IsStackEmpty()) return;
}
var v = new Node(term, col.Index - 1, col.Index)
{
AssociatedTerminal = token,
LogProbability = 0.0f,
Bits = 1
};
var y = State.MakeNode(state, col.Index, v);
var newState = new State(state.Rule, state.DotIndex + 1, state.StartColumn, y);
col.AddState(newState, ParsingOperation.Scan);
if (Debug)
Console.WriteLine("{0} & {1} & {2} & Scanned from State {3}, word: {4}\\\\", newState.StateNumber,
newState, col.Index,
state.StateNumber, token);
if (newState.Node.LogProbability < 0)
{
throw new LogException(string.Format("scanarrrr! NODE log probability lower than 0: {0}, state: {1}",
newState.Node.LogProbability, newState));
}
}
private void Complete(Column col, State state)
{
if (state.Rule.Name.NonTerminal == GammaRule)
{
col.GammaStates.Add(state);
return;
}
foreach (var st in state.StartColumn)
{
var term = st.NextProductionTerm();
NonTerminalStack intersection;
if (IsCompletedTermConsistentWithNextTerm(state.Rule.Name, term, out intersection))
{
if (state.Node.LogProbability < 0)
{
throw new LogException(
string.Format(
"trrrr! NODE log probability lower than 0: {0}, reductor state: {1}, predecessor state {2}",
state.Node.LogProbability, state, st));
}
var y = State.MakeNode(st, state.EndColumn.Index, state.Node);
var newState = new State(st.Rule, st.DotIndex + 1, st.StartColumn, y);
newState.Rule.Production[st.DotIndex].Stack = intersection;
col.AddState(newState, ParsingOperation.Complete);
if (Debug)
Console.WriteLine("{0} & {1} & {2} & Completed from States {3} and {4}\\\\",
newState.StateNumber,
newState, col.Index, st.StateNumber, state.StateNumber);
}
}
}
public static Node MakeNode(State predecessorState, int endIndex, Node reductor)
{
Node y;
var nextDotIndex = predecessorState.DotIndex + 1;
var nodeName = RuleWithDotNotation(predecessorState.Rule, nextDotIndex);
if (nextDotIndex == 1 && predecessorState.Rule.Production.Length > 1)
{
y = reductor;
if (predecessorState.Node == null)
{
y.LogProbability = predecessorState.LogProbability + reductor.LogProbability;
y.Bits = RequiredBitsGivenLogProbability(predecessorState.LogProbability) + reductor.Bits;
if (predecessorState.LogProbability < 0 || reductor.LogProbability < 0)
{
throw new Exception(
string.Format("first case y NODE log probability lower than 0: {0} < , {1} , {2}",
y.LogProbability, predecessorState.LogProbability, reductor.LogProbability));
}
}
else
throw new Exception("arrived in a clause that should not be possible. make_node");
}
else
{
y = new Node(nodeName, predecessorState.StartColumn.Index, endIndex);
if (!y.HasChildren())
y.AddChildren(reductor, predecessorState.Node);
if (predecessorState.Node == null)
{
y.LogProbability = predecessorState.LogProbability + reductor.LogProbability;
y.Bits = RequiredBitsGivenLogProbability(predecessorState.LogProbability) + reductor.Bits;
if (predecessorState.LogProbability < 0 || reductor.LogProbability < 0)
{
throw new Exception(
string.Format("second case y NODE log probability lower than 0: {0} = , {1} + {2}",
y.LogProbability, predecessorState.LogProbability, reductor.LogProbability));
}
}
else
{
y.LogProbability = predecessorState.Node.LogProbability + reductor.LogProbability;
y.Bits = predecessorState.Node.Bits + reductor.Bits;
if (predecessorState.Node.LogProbability < 0 || reductor.LogProbability < 0)
{
throw new Exception(
string.Format("third case y NODE log probability lower than 0: {0} = , {1} + {2}",
y.LogProbability, predecessorState.Node.LogProbability, reductor.LogProbability));
}
}
y.RuleNumber = predecessorState.Rule.Number;
}
return y;
}
