Ok, thanks to everyone, that's certainly answered my question and given me some more avenues to pursue. I can see now that because I can pattern match against the empty list it's not really a problem to have it there. I didn't realise I could use Maybe in the constructor because it's a monad, but that's good because I was wondering about the best way to make a nullable value. That Data.Tree module looks interesting too! It does seem to be a naturally recursive type, but I'm still trying to become easy with that sort of thought :) Thanks for all the help, it's nice to get a bit of feedback when still getting used to things. Iain
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