Well, either that or I being an idiot. Here's a little example. Let us say you had a datatype 'Month'* data Month = Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec deriving(Show, Eq, Ord, Ix) What I would like to make is an infinite lazy list of months (called, rather imaginitively I thought, 'months') that keeps wrapping around. That is to say, it would make a list like this [Jan, Feb, ...., Nov, Dec, Jan, Feb, ....., Nov, Dec, ... ad infinitum ] I am sure you get the picture. My first stab was this: months = range (Jan, Dec) : months But of course, what you get here is a list of lists, with each element being a list of [Jan, Feb, ...., Dec] So I puzzled for a little bit about how to do this in the most Haskelly way and I thought of this months = concat (range (Jan, Dec) : months) Which should work, right** But the type checker is not pleased at all and complains: Couldn't match expected type `[Month]' against inferred type `Month' Expected type: [[Month]] Inferred type: [Month] In the expression: concat (range (Jan, Dec) : months) In the definition of `months': months = concat (range (Jan, Dec) : months) However, if you use the first definition and make a second function: months = range (Jan, Dec) : months realmonths = concat(months) It is happy and does what one might expect. I thought perhaps I was just confusing the inference engine so I tried a liberal sprinkling of :: operators to make my intentions clear, but it still wasn't having any of it. Any thoughts welcomed! - Philip * I am aware that there is plenty of code to handle dates and times already written, probably much more nicely than mine - this is just a project I have been hacking at to get to grips with things. ** though I am pretty sure this is the Wrong Way to do this. I suspect concat takes O(n) time - more elegant approaches would be welcomed!