Today, I reviewed a function I wrote a few months ago. The function, dropTrailNulls, takes a list of lists and drops trailing null lists. For instance: *Main> dropTrailNulls [[1],[2,3],[],[]] [[1],[2,3]] My original implementation was terrible. It was recursive, overly bulky, and difficult to understand. It embarrasses me. I won't post it here. Today, it occurred to me this would do the trick: dropTrailNulls list = reverse (dropWhile null (reverse list)) The problem is 20 years of experience writing efficient imperative programs says to me, "You don't drop things off the end of a structure by reversing the structure, dropping stuff from the beginning, then reversing again." I suspect this imperative bias prevented me from coming up with the simple solution when I first wrote my function. On the other hand, it is conceivable to me that my new implementation may actually be relatively efficient since Haskell uses lazy evaluation, and Haskell lists are constructed from the tail to the beginning. I'm sure there are many problems that are encountered in Haskell where it is necessary to operate on the end of a list. So, I'm wondering if the idiom, reverse, operate, then reverse is something I should add to my toolbox. Or, is there a more efficient idiom for addressing these problems?