/// <summary>
/// Reads the next <see cref="Terminal"/>.
/// </summary>
/// <returns>The next <see cref="Terminal"/> in the input text. If no <see cref="TerminalType"/> recognizes the input text, <value>null</value> is returned.</returns>
public Terminal ReadTerminal()
{
Terminal result;
if (_queuedTerminal != null)
{
result = _queuedTerminal;
_queuedTerminal = null;
}
else
{
result = GetNextTerminal();
}
LinguaTrace.TraceEvent(TraceEventType.Information, LinguaTraceId.ID_PARSE_READTOKEN, "{0}", result);
return(result);
}
/// <summary>
/// Constructs a new <see cref="Parser"/> which can recoganize the specified <see cref="IGrammar"/>.
/// </summary>
/// <param name="grammar">The <see cref="IGrammar"/> to be recognized by the <see cref="Parser"/>.</param>
/// <returns>A <see cref="ParserGeneratorResult"/> containing <see cref="Parser"/> and information pertaining to the
/// success or failure of the generation process.
/// </returns>
public ParserGeneratorResult GenerateParser(IGrammar grammar)
{
List <ParserGeneratorParserConflict> conflicts = new List <ParserGeneratorParserConflict>();
List <GeneratorState> states = CreateStates(grammar);
// Create a parser state for each generator state.
//
Dictionary <GeneratorState, ParserState> parserStates = new Dictionary <GeneratorState, ParserState>();
foreach (GeneratorState state in states)
{
parserStates.Add(state, new ParserState(state.Id));
}
foreach (GeneratorState state in states)
{
LinguaTrace.TraceEvent(TraceEventType.Verbose, LinguaTraceId.ID_GENERATE_PROCESS_STATE, "{0}", state);
List <GeneratorStateItem> items = new List <GeneratorStateItem>(state.Items);
items.Sort();
// Construct the list of actions associated with the parser state.
//
Dictionary <TerminalType, ParserAction> actions = new Dictionary <TerminalType, ParserAction>();
Dictionary <ParserAction, GeneratorRuleItem> actionRules = new Dictionary <ParserAction, GeneratorRuleItem>();
foreach (GeneratorStateItem item in items)
{
LinguaTrace.TraceEvent(TraceEventType.Verbose, LinguaTraceId.ID_GENERATE_PROCESS_ITEM, "{0}", item);
if (item.RuleItem.DotElement == null)
{
foreach (TerminalType terminal in item.RuleItem.Rule.Lhs.Follow)
{
LinguaTrace.TraceEvent(TraceEventType.Verbose, LinguaTraceId.ID_GENERATE_PROCESS_TERMINAL, "{0}", terminal);
if (actions.ContainsKey(terminal))
{
ParserGeneratorParserConflict conflict = new ParserGeneratorParserConflict(
actionRules[actions[terminal]].ToString(),
item.RuleItem.ToString());
LinguaTrace.TraceEvent(TraceEventType.Information, LinguaTraceId.ID_GENERATE_PROCESS_CONFLICT, "{0}", conflict);
conflicts.Add(conflict);
}
else if (item.RuleItem.Rule.Lhs.IsStart &&
terminal.IsStop)
{
ParserAction action = new ParserActionAccept(item.RuleItem.Rule);
LinguaTrace.TraceEvent(TraceEventType.Information, LinguaTraceId.ID_GENERATE_PROCESS_ACTION, "{0}", action);
actions.Add(terminal, action);
actionRules.Add(action, item.RuleItem);
}
else
{
ParserAction action = new ParserActionReduce(item.RuleItem.Rule);
LinguaTrace.TraceEvent(TraceEventType.Information, LinguaTraceId.ID_GENERATE_PROCESS_ACTION, "{0}", action);
actions.Add(terminal, action);
actionRules.Add(action, item.RuleItem);
}
}
}
else if (item.RuleItem.DotElement.ElementType == LanguageElementTypes.Terminal)
{
TerminalType terminal = (TerminalType)item.RuleItem.DotElement;
if (actions.ContainsKey(terminal))
{
ParserGeneratorParserConflict conflict = new ParserGeneratorParserConflict(
actionRules[actions[terminal]].ToString(),
item.RuleItem.ToString());
LinguaTrace.TraceEvent(TraceEventType.Information, LinguaTraceId.ID_GENERATE_PROCESS_CONFLICT, "{0}", conflict);
conflicts.Add(conflict);
}
else
{
ParserAction action = new ParserActionShift(parserStates[state.Transitions[terminal]]);
LinguaTrace.TraceEvent(TraceEventType.Information, LinguaTraceId.ID_GENERATE_PROCESS_ACTION, "{0}", action);
actions.Add(terminal, action);
actionRules.Add(action, item.RuleItem);
}
}
}
// Construct the GOTO table
//
Dictionary <NonterminalType, ParserState> gotos = new Dictionary <NonterminalType, ParserState>();
foreach (KeyValuePair <LanguageElementType, GeneratorState> transition in state.Transitions)
{
if (transition.Key.ElementType == LanguageElementTypes.Nonterminal)
{
NonterminalType nonterminal = (NonterminalType)transition.Key;
gotos.Add(nonterminal, parserStates[transition.Value]);
}
}
// Update the parser state.
//
ParserState parserState = parserStates[state];
foreach (KeyValuePair <TerminalType, ParserAction> action in actions)
{
parserState.Actions.Add(action.Key, action.Value);
}
foreach (KeyValuePair <NonterminalType, ParserState> gotoItem in gotos)
{
parserState.Gotos.Add(gotoItem.Key, gotoItem.Value);
}
}
Parser parser = new Parser(parserStates[states[0]]);
ParserGeneratorResult result = new ParserGeneratorResult(parser, conflicts);
return(result);
}
private List <GeneratorState> CreateStates(IGrammar grammar)
{
List <GeneratorState> states = new List <GeneratorState>();
List <GeneratorState> unevaluatedStates = new List <GeneratorState>();
int stateId = 0;
// Compute start state.
//
{
HashSet <GeneratorStateItem> items = new HashSet <GeneratorStateItem>();
foreach (RuleType rule in grammar.StartNonterminal.Rules)
{
items.Add(new GeneratorStateItem(new GeneratorRuleItem(rule, 0)));
}
ComputeClosure(grammar, items);
GeneratorState startState = new GeneratorState(stateId++, items);
states.Add(startState);
unevaluatedStates.Add(startState);
}
List <LanguageElementType> languageElements = new List <LanguageElementType>();
languageElements.AddRange(grammar.GetTerminals());
languageElements.AddRange(grammar.GetNonterminals());
while (unevaluatedStates.Count > 0)
{
// Remove one of the evaluated states and process it.
//
GeneratorState state = unevaluatedStates[0];
unevaluatedStates.RemoveAt(0);
foreach (LanguageElementType languageElement in languageElements)
{
HashSet <GeneratorStateItem> items = state.Apply(languageElement);
if (items != null)
{
ComputeClosure(grammar, items);
GeneratorState toState = null;
foreach (GeneratorState existingState in states)
{
if (existingState.Items.SetEquals(items))
{
toState = existingState;
break;
}
}
if (toState == null)
{
toState = new GeneratorState(stateId++, items);
states.Add(toState);
unevaluatedStates.Add(toState);
}
state.Transitions.Add(languageElement, toState);
}
}
}
if (LinguaTrace.TraceSource.Switch.ShouldTrace(TraceEventType.Information))
{
foreach (GeneratorState state in states)
{
LinguaTrace.TraceEvent(TraceEventType.Information, LinguaTraceId.ID_GENERATE_STATE, "{0}", state);
}
}
return(states);
}
/// <summary>
/// Performs syntax analysis against a sequence of terminals according to the <see cref="Grammar"/> used to create the <see cref="Parser"/>.
/// </summary>
/// <param name="terminalReader">Retrieves a sequence of <see cref="Terminal"/> objects.</param>
/// <returns>If syntax analysis succeeds, returns the <see cref="Nonterminal"/> associated with <see cref="Grammar.StartNonterminal"/>. Otherwise, <value>null</value> is returned.</returns>
public Nonterminal Parse(ITerminalReader terminalReader)
{
var stack = new ParserStack();
stack.Push(null, InitialState);
var terminal = terminalReader.ReadTerminal();
while (terminal != null)
{
if (terminal.ElementType.Ignore)
{
terminal = terminalReader.ReadTerminal();
}
else
{
var action = stack.Peek().State.GetAction(terminal.ElementType);
LinguaTrace.TraceEvent(TraceEventType.Information, LinguaTraceId.ID_PARSE_ACTION, "{0}", action);
if (action == null)
{
return(null);
}
switch (action.ActionType)
{
case ParserActionTypes.Accept:
{
var reduce = (ParserActionAccept)action;
var rule = reduce.Rule;
var lhs = Reduce(stack, rule);
return(lhs);
}
case ParserActionTypes.Shift:
{
var shift = (ParserActionShift)action;
stack.Push(terminal, shift.State);
terminal = terminalReader.ReadTerminal();
}
break;
case ParserActionTypes.Reduce:
{
var reduce = (ParserActionReduce)action;
var rule = reduce.Rule;
var lhs = Reduce(stack, rule);
// Push the LHS nonterminal on the stack.
//
stack.Push(lhs, stack.Peek().State.GetGoto(lhs.ElementType));
}
break;
default:
throw new InvalidOperationException(string.Format("Unrecognized action type {0}.", action.ActionType));
}
}
}
return(null);
}
