/// 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);
}
