You (Graham) also have some parentheses issues; e.g. in foo ++ (combinations 5 l) the parentheses are superfluous.
I'm tempted to argue that being superfluous doesn't mean they shouldn't be there. This isn't just a functional programming issue... I find that when there are many levels of operator precedence it's easier to be explicit than to try and remember what they all are -- as much for reading the code as writing it in the first place. But maybe I'm still reading functional code in the wrong way? (I still scratch my head over some of the prelude/library functions, though it's getting easier.)
This is a particular instance where you never need the parentheses... since it's a _functional_ language, _function application_ (the invisible symbol between combinations and 5, and between combinations 5 and l) binds tighter than anything else. The only time you need parentheses around a function application are when it is to protect it from a competing function application, such as when you are passing it as an argument to a function: map (map f) xss rather than map map f xss HTH. --KW 8-)