/// <name>ForwardReference</name>
/// <type>Constructor</type>
/// <summary>
/// Creates a new forward reference object with initialization.
/// </summary>
/// <param name="instructionLocation">Instruction initialization parameter</param>
/// <param name="reference">Reference symbol parameter</param>
public ForwardReference(int instructionLocation, Symbol reference)
: base()
{
this.instructionLocation = instructionLocation;
this.reference = reference;
}
/// <name>Parser</name>
/// <type>Constructor</type>
/// <summary>
/// Creates a parser object.
/// </summary>
public Parser()
: base()
{
// Initalize class variables
currentOperator = new Token(TokenType.NO_TOKEN, String.Empty);
nextOperator = new Token(TokenType.NO_TOKEN, String.Empty);
operand = null;
literal = null;
symbol = null;
inExpression = false;
nextLocation = 1;
symbolTable = new Dictionary<string, Symbol>();
literalTable = new Dictionary<string, Literal>();
operatorStack = new Stack<Token>();
structureStack = new Stack<Structure>();
forwardRefStack = new Stack<ForwardReference>();
}
/// <name>Advance</name>
/// <type>Method</type>
/// <summary>
/// Advances the current and next operators from the input file and
/// populates the operand token between the operators if one exists.
/// </summary>
private void Advance()
{
// Advance one token
currentOperator = (Token)nextOperator.Clone();
Token peekToken = source.GetNextToken();
// Make sure operand, symbol and literal are null
operand = null;
symbol = null;
literal = null;
if (peekToken.Type == TokenType.SYMBOL)
{
// If the new token is a symbol then set operand to that token
operand = (Token)peekToken.Clone();
// Now check to see if the symbol is already defined - if
// it is then assign to symbol, otherwise add it to the table
if (symbolTable.ContainsKey(peekToken.Lexeme))
{
symbol = symbolTable[peekToken.Lexeme];
}
else
{
symbolTable.Add(peekToken.Lexeme, new Symbol(peekToken.Lexeme));
symbol = symbolTable[peekToken.Lexeme];
}
// Finally get the next token
nextOperator = source.GetNextToken();
}
else if (peekToken.Type == TokenType.LITERAL)
{
// If the new token is a literal then set operand to that token
operand = (Token)peekToken.Clone();
// Now check to see if the literal is already defined - if
// it is then assign to literal, otherwise add it to the table
if (literalTable.ContainsKey(peekToken.Lexeme))
{
literal = literalTable[peekToken.Lexeme];
}
else
{
literalTable.Add(peekToken.Lexeme, new Literal(peekToken.Lexeme));
literal = literalTable[peekToken.Lexeme];
}
// Finally get the next token
nextOperator = source.GetNextToken();
}
else
{
// Set the next operator to the token we just retrieved
nextOperator = (Token)peekToken.Clone();
}
// Output debug information
Compiler.WriteToDebug("Parser - Advance called (line " + Compiler.LineNumber + ")");
Compiler.WriteToDebug(" current operator:\t" + currentOperator.Lexeme);
if (operand != null)
{
Compiler.WriteToDebug(" operand:\t\t" + operand.Lexeme);
}
Compiler.WriteToDebug(" next operator:\t" + nextOperator.Lexeme);
Compiler.WriteToDebug(String.Empty);
}
/// <name>CompileProcedures</name>
/// <type>Method</type>
/// <summary>
/// Compile program procedures.
/// </summary>
private void CompileProcedures()
{
status = Status.CONTINUE;
// If there's a procedure declaration in the program then we need a new
// symbol to define the start on the main program's execution when we get
// to it, so create the symbol now and save it as a forward reference
if (nextOperator.Type == TokenType.PROC)
{
Symbol main = new Symbol("$MAIN");
symbolTable.Add(main.Lexeme, main);
SaveForwardReference(main, jvm.ProgramCounter);
jvm.Emit(Opcode.GOTO, 0);
}
// Keep going until the end block of the program structure is reached
while (structureStack.Count > 0)
{
CodeGenerator(currentOperator, nextOperator);
Advance();
}
// Pop the forward references left and fill with the appropriate address
FillForwardReferences();
}
/// <name>SaveForwardReference</name>
/// <type>Method</type>
/// <summary>
/// Push a forward reference onto the stack. This contains a symbol
/// whose actual address in the code is not yet known.
/// </summary>
/// <param name="reference">Reference symbol</param>
/// <param name="address">Address of the reference symbol</param>
private void SaveForwardReference(Symbol reference, int address)
{
forwardRefStack.Push(new ForwardReference(address, reference));
}