public List <Step> ParseTokens() // Due to the size of this method I am not using IEnumerable 'yield return' as it is hard to track nested return statements.
{
List <Step> EvaluationSteps = new List <Step>();
while (tokQueue.More()) // While more tokens in queue (returns bool)
{
Token nextTok = tokQueue.MoveNext(); // pop next out of TokenQueue
if (nextTok.Type().Equals("identifier"))
// All statements in our language begin with identifiers.
// We do not know what we have at this point, so let's check the identifier to see which tokens should follow after.
{
if (Syntax.IsType(nextTok.Value()))
// If it is a var type, e.g "int", "string" - if it is, this is a variable declaration ("int x = 0;")
{
/*
* EXPECTED PATTERN: varType varName = expr;
* e.g int x = 2 + y*10;
* e.g string testing = "Hello World!";
*/
VarDeclare varDeclare = CaptureVarDeclare(nextTok.Value()); // Call method with argument storing the type of var being declared, e.g 'string'
EvaluationSteps.Add(varDeclare); // Add Event object to the overall list of 'Steps' for the Evaluator module
}
else if (nextTok.Value().ToLower().Equals("if"))
// Start of an if statement
{
/*
* EXPECTED PATTERN: if(operands) { codeblock }
* e.g if (x > 0) {
* output(x);
* x = 0;
* }
*/
IfStatement ifState = CaptureIfStatement(); // Capture all useful information of the following if statements
// We COULD have an else statement, so let's check the next token
// First check there are still MORE tokens to check to avoid out of range errors
// Then check it's an IDENTIFIER ('else')
if (tokQueue.More() && tokQueue.Next().Type().Equals("identifier") && tokQueue.Next().Value().Equals("else"))
{
// If next token is 'else' and an identifier
ElseStatement elseState = CaptureElseStatement();
EvaluationSteps.Add(ifState);
EvaluationSteps.Add(elseState);
// Add if state then else directly after (ordered list!)
}
else
{
EvaluationSteps.Add(ifState); // if no 'else' statement exists just add the if statement
}
}
else if (nextTok.Value().ToLower().Equals("while"))
{
IfStatement template = CaptureIfStatement(); // Trick the program to think it's capturing an if statement
WhileLoop whileLoop = new WhileLoop(template.GetCBContents(), template.GetOp1(), template.GetOp2(), template.GetComparator());
// Reuse code from the if statement because while & if follow the exact same structure:
// while (condition) { codeblock }
// if (condition) { codeblock }
// We just captured an if statement 'template' then used the information it collected to create a while loop instead
EvaluationSteps.Add(whileLoop);
}
else if (GrammarTokenCheck(tokQueue.Next(), "("))
// This condition will also return true if it finds an if/while statement, so it is AFTER the check for those.
// As we're using else if, if the program didn't recognise a 'while' or 'if' statement, we will reach this check
// We can GUARANTEE now that this must be a function call as 'if(){}' and 'while(){}' have been ruled out
{
/*
* EXPECTED PATTERN: funcName(expr); // Can take any expression!
* e.g output("Testing");
* e.g output(1 + 23);
* e.g output(x);
*/
tokQueue.MoveNext(); // Skip the '(' token
// Remember, nextTok still holds the value of the token before '('
// This is the name of our function ('funcName')
FuncCall funcCall = CaptureFunctionCall(nextTok.Value()); // Pass the function name, e.g 'output'
EvaluationSteps.Add(funcCall);
}
else if (GrammarTokenCheck(tokQueue.Next(), "=")) // .Next() is PEEK not POP.
// Check if the token AFTER this one is "="
{
/*
* EXPECTED PATTERN: varName = expr;
* e.g x = 2 + y*10;
* e.g testing = "Hello World!";
*/
tokQueue.MoveNext(); // Skip the '=' token
// Remember, nextTok still holds the value of the token before the '='
// This is the name of our variable to change ('varName')
VarChange varChan = CaptureVarChange(nextTok.Value());
EvaluationSteps.Add(varChan);
}
else
{
throw new SyntaxError();
}
// If there is a rogue 'else' statement it will be caught in this
// Else statements are not 'looked' for on there own, they are only recognised when an if statement is found
}
else
{
throw new SyntaxError(); // Statement doesn't begin with identifier - throw error.
}
}
return(EvaluationSteps);
}
