Practically, the way to go here is: make your data structures strict (with "!") and make your control structures lazy. So, don't create a list of numbers if yo

Practically, the way to go here is: make your data structures strict (with "!") and make your control structures lazy. So, don't create a list of numbers if you intend to sum it, use a non- lazy data structure. The trick is that Haskell's common default structures are lazy.