If this interpreter is going to become part of your portfolio, I highly recommend you communicate that fact early. That way, you can get feedback, and improve your work before submission.
When I look at your code, I'll consider the following:
- Did you write code in the style that is presented in HtDP, and exemplified in the solutions I have provided to you this semester?
- Have you torn the code up (much like we do in code walks) and done your best to make it truly excellent?
- Are your tests thorough? Do they exercise all of your code? Could there be more? ("More" does not mean "repetitious." It is just a question of whether there are more cases you haven't considered.)
- Have you given credit properly where help was received?
In short, if you are doing work that will become part of your portfolio, it should be excellent. This is doubly-true if you are working as a pair—you have two brains to tackle these problems.