private FunctionDefinition ParseLambdaHelperStart(string name) {
var start = GetStart();
Parameter[] parameters;
parameters = ParseVarArgsList(TokenKind.Colon);
var mid = GetEnd();
FunctionDefinition func = new FunctionDefinition(name, parameters ?? new Parameter[0]); // new Parameter[0] for error handling of incomplete lambda
func.HeaderIndex = mid;
func.StartIndex = start;
// Push the lambda function on the stack so that it's available for any yield expressions to mark it as a generator.
PushFunction(func);
return func;
}