In the same boat of not knowing Haskell, this is how I interpreted it - the [[]] denotes a nested array of ints, where each array represents a set of variable v

In the same boat of not knowing Haskell, this is how I interpreted it - the [[]] denotes a nested array of ints, where each array represents a set of variable values on 0..26 that satisfy all guards. Guard $ foo Is equivalent to filtering out the values in u in each variable that fails foo. They're staged that way for the sake of performance - filter out possible values of x now so that the next guard statement has fewer possibilities to iterate over. Then, once all guard statements have been put into effect, the full set of combinations of values that pass each guard are placed in the array. Critically, it is not "for u in [0..26]" but "u=[0..26]", which gives me the idea that this isn't a loop but a filter.