public static void Run()
{
Tokeniser tokeniser = new Tokeniser(Console.ReadLine());
List <Token> tokens = tokeniser.Tokenise().ToList();
TreeNode bin1 = TreeBuilder.BuildAST(tokens); // e.g "5 * 2 + 1" -> "5 2 * 1 +"
// Using TreeNode type, not BinOp (Binary Operator) as we cannot guarantee the root node of the abstract syntax tree will be an operator.
Console.WriteLine("To postfix:");
foreach (TreeNode node in Traversal.postOrder(bin1))
{
Console.Write(node.value + " ");
}
Console.WriteLine("\nTo infix:");
foreach (TreeNode node in Traversal.inOrder(bin1))
{
Console.Write(node.value + " ");
}
Console.WriteLine("\nTo prefix:");
foreach (TreeNode node in Traversal.preOrder(bin1))
{
Console.Write(node.value + " ");
}
Console.WriteLine();
// Now using reverse polish notation, calculate what the result is. This takes in a postfix-ordered list of TreeNodes.
Console.WriteLine("Answer: " + RPN.Evaluate(Traversal.postOrder(bin1)));
}
public Token ResolveExpression(List <Token> expr) // TODO
{
Token toReturn = new Token("", "");
// First, replace variable name references with their values.
expr = VariablesToValues(expr);
// Now check tokens are all the same type in the expression (except grammar tokens)
string exprResultType = CheckTypes(expr); // This func will throw error if they aren't
// exprResultType now stores the final expected type for when expression is resolved to one token
// e.g 1 + 1 => resolves to 'number'
// e.g "1" + "1" => resolves to 'string'
if (exprResultType.Equals("string"))
// Indicates that we are dealing with a string expression
{
// The only operation that can be done to strings in an expression is '+' for concat
if (expr.Count == 1)
{
toReturn = new Token("string", expr[0].Value());
}
// If there is only one token in the whole expression, it must just be a string
// Therefore we can just return the string as it's 1 token
else
{
// We must be dealing with concatenation
if (!expr[0].Type().Equals("string"))
{
throw new SyntaxError();
}
// Concatenation expressions MUST start with a string
// e.g string x = + "Hello World"; will cause ERROR as expr starts with '+'
string finalResult = expr[0].Value(); // First string in expression
int index = 1;
while (index < expr.Count)
{
if (expr[index].Type().Equals("operator"))
{
if (expr[index].Value().Equals("+") && index < expr.Count - 1)
{
finalResult += expr[index + 1].Value(); // Add NEXT string to final result
}
else
{
throw new TypeMatchError(); // Cannot do any other operation than '+' on strings
}
}
index++;
}
toReturn = new Token("string", finalResult);
}
}
else if (exprResultType.Equals("number"))
// Indicates we are dealing with a mathematical expression
{
TreeNode root = TreeBuilder.BuildAST(expr); // Create abstract syntax tree of mathematical expression
int result = RPN.Evaluate(Traversal.postOrder(root)); // Calculate result of RPN algorithm calculation
toReturn = new Token("number", result.ToString());
}
else
{
throw new SyntaxError(); // invalid expression type has somehow made it through, we cannot evaluate it so throw error.
}
return(toReturn);
}