These are nifty assignments. I am particularly tempted to tackle the tree-list recursion problem at some point. It seems like the sort of thing that would be fun to invite some friends over for dinner around - good food, throw up a projector, have everyone poke at it together... no, you don't actually need other people to solve it, but I recall how dwins and I and a few others at TOPP went through learning Haskell once, and I do think that would make for a nice social evening.
Instead of bowling with friends, try list-recursion or Haskell with friends, or go see a lecture on web platforms at MIT. Instead of walking around the mall looking at clothing, walk around You-Do-It/Fry's ogling electronics equipment, or even Home Depot, grabbing wood and nails and glue and drill bits with which to make something - boats, lofts, anything. Cooking parties - three of the most delicious meals I've ever had during my college years were making fresh pasta and then pasta carbonara with David Yoshida to try out his new pasta machine, and then when Cathy Murphie decided she was going to teach a few of us how to bake French bread, and then again when Chris and Beth and I made dinner for Debbie Chachra as the final deliverable for our Passionate Pursuit from cooking classes (pears poached in red wine == NOM). Painting parties - coloring the walls of our skechtacular apartment in Somerville right after graduation. Random design competitions. These are the things I like doing with my friends. I like making things with my friends.
I always feel a little weird in purely-social parties where it's pretty much all beer and music... aside from the music tending to be extremely loud (ouch) and the beer tending to be not so much my thing, they tend to be too dark for lipreading, and... they make me tired. I end up in a quiet corner by myself, reading, sketching, thinking, watching people. I mean, I like music, and I tend to play it loud (because I can't hear as well as most people), but I appreciate it for the music, not the furniture-shaking decibels. I like beer, but... in small quantities, for the interesting flavor combinations when combined with food with alcohol-soluble components, and I don't like the feeling of being even mildly inebriated. I sometimes try to bring a tiny portable collaboration-friendly thing-to-tinker-with to those, but haven't hit on much of a good one yet - a notebook seems to be the best so far, for collaborative sketching/brainstorming/passing-of-notes. I... am shy. And I would really rather just make stuff.
I don't know if other people feel this way - it's one of those things that my mother will sometimes complain about ("you just want to do work, why don't you go out with friends?") to which I respond that my teammates are often my friends and vice versa, and that this sort of work is fun and satisfying and relaxing. I get the impression that they think I have no social life and that I'm a hermit-like engineer. Which... okay, in one sense, sure - in a lot of ways, work is my life. Work, not necessarily $dayjob. But in another sense, this is my social life. And I find it satisfying rather than "sad" - I'm learning how to balance it, learning how to relax and rest more - but... I mean, this makes me happy. I am not sure how to convey that to them. Trying to figure it out. I think they know it makes me happy (I hope so - I mean, it's pretty obvious when I am happy; Nikki tells me my happy is loud) but I am not sure they know why. And I am not sure that it matters that they do know why - it's something I'd like, though.
Anyway. Just musing.
 Not that things like bowling/movies/theatre/karaoke/etc aren't fun - they are - but I think these things are fun too.