The use of elem is certainly more concise. But this isn't quite right (Hugs rejects it):
isYes = `elem` ["y", "yes", "Y", "YES"]
I think what's meant is: isYes = flip elem ["y", "yes", "Y", "YES"] and agree that isYes = flip elem ["y", "yes"] . (map toLower) is even better.
Of course, the very last "if" could be,
if isYes playAgain then play rewrittenNode else putStr "Goodbye for now."
I had it the other way around because of a vague notion about tail-recursion that perhaps doesn't apply here? It's useful to know where "do"s and parentheses are not needed. I agree about records; I thought they would be useful, and ended up not using them. Derek's use of LiftM is new to me, as most things in Haskell are. The @ operator (fullstring@(c:cs)) looks very handy. Thanks to all, Dominic