private SimpleASTNode Multiplicative(TokenReader tokens)
{
SimpleASTNode child1 = Primary(tokens);
SimpleASTNode node = child1;
while (true)
{
Token token = tokens.Peek();
if (token != null && (token.GetType() == TokenType.Star || token.GetType() == TokenType.Slash))
{
token = tokens.Read();
SimpleASTNode child2 = Primary(tokens);
if (child2 != null)
{
node = new SimpleASTNode(ASTNodeType.Multiplicative, token.GetText());
node.AddChild(child1);
node.AddChild(child2);
child1 = node;
}
else
{
throw new Exception("invalid multiplicative expression, expecting the right part.");
}
}
else
{
break;
}
}
return(node);
}
/// <summary>
/// 解析加法表达式
/// </summary>
/// <param name="tokens"></param>
/// <returns></returns>
private SimpleASTNode Additive(TokenReader tokens)
{
SimpleASTNode child1 = Multiplicative(tokens);
SimpleASTNode node = child1;
Token token = tokens.Peek();
if (child1 != null && token != null)
{
if (token.GetType() == TokenType.Plus || token.GetType() == TokenType.Minus)
{
token = tokens.Read();
SimpleASTNode child2 = Additive(tokens);
if (child2 != null)
{
node = new SimpleASTNode(ASTNodeType.Additive, token.GetText());
node.AddChild(child1);
node.AddChild(child2);
}
else
{
throw new Exception("invalid additive expression, expecting the right part.");
}
}
}
return(node);
}
private SimpleASTNode Additive2(TokenReader tokens)
{
SimpleASTNode child1 = Multiplicative(tokens);
SimpleASTNode node = child1;
if (child1 != null)
{
while (true)
{
Token token = tokens.Peek();
if (token != null && (token.GetType() == TokenType.Plus || token.GetType() == TokenType.Minus))
{
token = tokens.Read();
SimpleASTNode child2 = Multiplicative(tokens);
node = new SimpleASTNode(ASTNodeType.Additive, token.GetText());
node.AddChild(child1);
node.AddChild(child2);
child1 = node;
}
else
{
break;
}
}
}
return(node);
}
/// <summary>
/// 根节点
/// </summary>
/// <param name="tokens"></param>
/// <returns></returns>
private SimpleASTNode Prog(TokenReader tokens)
{
SimpleASTNode node = new SimpleASTNode(ASTNodeType.Program, "Caculator");
SimpleASTNode child = Additive2(tokens);
if (child != null)
{
node.AddChild(child);
}
return(node);
}
/// <summary>
/// 声明变量
/// int a
/// int b = 2 * 3
/// </summary>
/// <param name="tokens"></param>
/// <returns></returns>
private SimpleASTNode IntDeclare(TokenReader tokens)
{
SimpleASTNode node = null;
Token token = tokens.Peek();
if (token != null && token.GetType() == TokenType.Int)
{
token = tokens.Read();
if (tokens.Peek().GetType() == TokenType.Identifier)
{
token = tokens.Read();
node = new SimpleASTNode(ASTNodeType.IntDeclaration, token.GetText());
token = tokens.Peek();
if (token != null && token.GetType() == TokenType.Assignment)
{
tokens.Read();
SimpleASTNode child = Additive(tokens);
if (child == null)
{
throw new Exception("invalid variable iniialization, expecting an expression.");
}
else
{
node.AddChild(child);
}
}
}
else
{
throw new Exception("Variable name expected.");
}
}
if (node != null)
{
token = tokens.Peek();
if (token != null && token.GetType() == TokenType.SemiColon)
{
tokens.Read();
}
else
{
throw new Exception("invalid statement, expecting semicolon");
}
}
return(node);
}
private SimpleASTNode AssignmentStatement(TokenReader tokens)
{
SimpleASTNode node = null;
Token token = tokens.Peek();
if (token != null && token.GetType() == TokenType.Identifier)
{
token = tokens.Read();
node = new SimpleASTNode(ASTNodeType.AssignmentStmt, token.GetText());
token = tokens.Peek();
if (token != null && token.GetType() == TokenType.Assignment)
{
tokens.Read();
SimpleASTNode child = Additive(tokens);
if (child == null)
{
throw new Exception("invalid assignment statement, expecting an expression");
}
else
{
node.AddChild(child);
token = tokens.Peek();
if (token != null && token.GetType() == TokenType.SemiColon)
{
tokens.Read();
}
else
{
throw new Exception("invalid statement, expecting semicolon");
}
}
}
else
{
tokens.UnRead();
node = null;
}
}
return(node);
}