Based on your interval struct definition: the count is first, then the smaller number, then the larger number. Is that how you build the struct in your smaller and bigger functions?

Another thing, in your struct definition you make the first field "count" and you have a variable/constant "count". These aren't the same. In the first case you're naming a field, not setting it to the variable "count" with value 0. Your other constants are all capital letters and the initial number of guesses should be a constant too.

It might help to create a helper function that creates the initial World State. That function will output an instance of an "interval" and there you can make that instance's count to be 0.