/// <summary>Adds an new LRAction to this table.</summary>
/// <param name="p_symbol">The Symbol.</param>
/// <param name="p_action">The Action.</param>
/// <param name="p_value">The value.</param>
public void AddItem(Symbol p_symbol, Action p_action, int p_value)
{
LRAction item = new LRAction();
item.Symbol = p_symbol;
item.Action = p_action;
item.Value = p_value;
m_members.Add(item);
}
/// <summary>Produces a reduction.</summary>
/// <remarks>Removes as many tokens as members in the rule and pushes a
/// non-terminal token.</remarks>
private ParseResult Reduce(Rule p_rule)
{
ParseResult result;
Token head;
if (m_trimReductions && p_rule.ContainsOneNonTerminal)
{
// The current rule only consists of a single nonterminal and can be trimmed from the
// parse tree. Usually we create a new Reduction, assign it to the Data property
// of Head and push it on the stack. However, in this case, the Data property of the
// Head will be assigned the Data property of the reduced token (i.e. the only one
// on the stack). In this case, to save code, the value popped of the stack is changed
// into the head.
head = m_tempStack.PopToken();
head.SetParent(p_rule.RuleNonTerminal);
result = ParseResult.ReduceEliminated;
}
else
{
Reduction reduction = new Reduction();
reduction.ParentRule = p_rule;
m_tempStack.PopTokensInto(reduction, p_rule.SymbolCount);
head = new Token();
head.Data = reduction;
head.SetParent(p_rule.RuleNonTerminal);
m_haveReduction = true;
result = ParseResult.ReduceNormal;
}
int index = m_tempStack.PeekToken().State;
LRAction action = m_LalrTables[index].GetActionForSymbol(p_rule.RuleNonTerminal.TableIndex);
if (action != null)
{
head.State = m_LalrState = action.Value;;
m_tempStack.PushToken(head);
}
else
{
throw new ParserException("Action for LALR state is null");
}
return(result);
}
/// This function analyzes a token and either:
/// 1. Makes a SINGLE reduction and pushes a complete Reduction object on the stack
/// 2. Accepts the token and shifts
/// 3. Errors and places the expected symbol indexes in the Tokens list
/// The Token is assumed to be valid and WILL be checked
private ParseResult ParseToken(Token p_token)
{
ParseResult result = ParseResult.InternalError;
LRActionTable table = m_LalrTables[m_LalrState];
LRAction action = table.GetActionForSymbol(p_token.TableIndex);
if (action != null)
{
m_haveReduction = false;
m_outputTokens.Clear();
switch (action.Action)
{
case Action.Accept:
m_haveReduction = true;
result = ParseResult.Accept;
break;
case Action.Shift:
p_token.State = m_LalrState = action.Value;
m_tempStack.PushToken(p_token);
result = ParseResult.Shift;
break;
case Action.Reduce:
result = Reduce(m_rules[action.Value]);
break;
}
}
else
{
// syntax error - fill expected tokens.
m_outputTokens.Clear();
foreach (LRAction a in table.Members)
{
SymbolType kind = a.Symbol.Kind;
if (kind == SymbolType.Terminal || kind == SymbolType.End)
{
m_outputTokens.PushToken(new Token(a.Symbol));
}
}
result = ParseResult.SyntaxError;
}
return(result);
}
