/// This method implements the DFA algorithm and returns a token
/// to the LALR state machine.
private Token RetrieveToken()
{
Token result;
int currentPos = 0;
int lastAcceptState = -1;
int lastAcceptPos = -1;
FAState currentState = m_DfaStates[m_initDfaState];
try
{
while (true)
{
// This code searches all the branches of the current DFA state for the next
// character in the input LookaheadStream. If found the target state is returned.
// The InStr() function searches the string pCharacterSetTable.Member(CharSetIndex)
// starting at position 1 for ch. The pCompareMode variable determines whether
// the search is case sensitive.
int target = -1;
char ch = FixCase(m_source.LookAhead(currentPos));
foreach (FAEdge edge in currentState.Edges)
{
String chars = edge.Characters;
if (chars.IndexOf(ch) != -1)
{
target = edge.TargetIndex;
break;
}
}
// This block-if statement checks whether an edge was found from the current state.
// If so, the state and current position advance. Otherwise it is time to exit the main loop
// and report the token found (if there was it fact one). If the LastAcceptState is -1,
// then we never found a match and the Error Token is created. Otherwise, a new token
// is created using the Symbol in the Accept State and all the characters that
// comprise it.
if (target != -1)
{
// This code checks whether the target state accepts a token. If so, it sets the
// appropiate variables so when the algorithm is done, it can return the proper
// token and number of characters.
if (m_DfaStates[target].AcceptSymbol != -1)
{
lastAcceptState = target;
lastAcceptPos = currentPos;
}
currentState = m_DfaStates[target];
currentPos++;
}
else
{
if (lastAcceptState == -1)
{
result = new Token(m_errorSymbol);
result.Data = m_source.Read(1);
}
else
{
Symbol symbol = m_symbols[m_DfaStates[lastAcceptState].AcceptSymbol];
result = new Token(symbol);
result.Data = m_source.Read(lastAcceptPos + 1);
}
break;
}
}
}
catch (EndOfStreamException)
{
result = new Token(m_endSymbol);
result.Data = "";
}
UpdateLineNumber((String)result.Data);
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;
}
/// <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;
}
/// Returns true if the specified token is a CommentLine or CommentStart-symbol.
private bool CommentToken(Token p_token)
{
return (p_token.Kind == SymbolType.CommentLine)
|| (p_token.Kind == SymbolType.CommentStart);
}
private void PrepareToParse()
{
Token token = new Token();
token.State = m_initLalrState;
token.SetParent(m_symbols[m_startSymbol]);
m_tempStack.PushToken(token);
}
/* public methods */
/// Pushes the specified token onto the internal input queue.
/// It will be the next token analyzed by the parsing engine.
public void PushInputToken(Token p_token)
{
m_inputTokens.PushToken(p_token);
}
/// Pushes the specified token on the stack.
public void PushToken(Token p_token)
{
m_items.Add(p_token);
}
/* internal methods */
///
internal void AddToken(Token p_token)
{
m_tokens.Add(p_token);
}
