public NullExpressionNode(NullLiteralNode stringLiteral, SourceCodePosition pos) : base(pos)
{
NullLiteral = stringLiteral;
}
public object Visit(NullLiteralNode n, object o)
{
return(null);
}
public Word Visit(NullLiteralNode nullLiteralNode)
{
return(MyNull.GetInstance());
}
public object Visit(NullLiteralNode n, object o)
{
Append(n.Value);
return(null);
}
private ExpressionNode Primary()
{
ExpressionNode itsAST = null; // in case there is a syntactic error
SourceCodePosition itsPos = _currentToken.SourcePosition;
if (_currentToken.Type == Token.TokenType.LeftParen)
{
Accept(Token.TokenType.LeftParen);
itsAST = Expression();
Accept(Token.TokenType.RightParen);
}
else if (Array.Exists(_literalFirstSet, e => e == _currentToken.Type))
{
switch (_currentToken.Type)
{
case Token.TokenType.IntLiteral:
IntLiteralNode intLiteral = new IntLiteralNode(_currentToken.Value, _currentToken.SourcePosition);
Accept(Token.TokenType.IntLiteral);
itsAST = new IntExpressionNode(intLiteral, itsPos);
break;
case Token.TokenType.RealLiteral:
RealLiteralNode realLiteral = new RealLiteralNode(_currentToken.Value, _currentToken.SourcePosition);
Accept(Token.TokenType.RealLiteral);
itsAST = new RealExpressionNode(realLiteral, itsPos);
break;
case Token.TokenType.StringLiteral:
StringLiteralNode stringLiteral = new StringLiteralNode(_currentToken.Value, _currentToken.SourcePosition);
Accept(Token.TokenType.StringLiteral);
itsAST = new StringExpressionNode(stringLiteral, itsPos);
break;
case Token.TokenType.BooleanLiteral:
BooleanLiteralNode booleanLiteral = new BooleanLiteralNode(_currentToken.Value, _currentToken.SourcePosition);
Accept(Token.TokenType.BooleanLiteral);
itsAST = new BooleanExpressionNode(booleanLiteral, itsPos);
break;
case Token.TokenType.Null:
NullLiteralNode nullLiteral = new NullLiteralNode(_currentToken.Value, _currentToken.SourcePosition);
Accept(Token.TokenType.Null);
itsAST = new NullExpressionNode(nullLiteral, itsPos);
break;
default:
itsAST = null; // should not happen
break;
}
}
else if (_currentToken.Type == Token.TokenType.Identifier)
{
itsAST = MemberReference();
}
else if (_currentToken.Type == Token.TokenType.This)
{
itsAST = ThisReference();
}
else if (_currentToken.Type == Token.TokenType.New)
{
itsAST = Instantiation();
}
else
{
Error("The token is invalid in the current context");
}
return(itsAST);
}
