Jeff.Harper@handheld.com wrote:
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]]
dropTrailNulls = foldr dtn [] where dtn [] [] = [] dtn x xs = x:xs
dropTrailNulls list = reverse (dropWhile null (reverse list))
As the other responses said, this is needlessly strict. Work on deforesting reverse exists, but you can't count on it happenig.
is there a more efficient idiom for addressing these problems?
Well, there's always the basic fold. I'm not sure there's any lesson to be learnt here other than "fold is your friend". Udo. -- F: Was ist ansteckend und kommutiert? A: Eine Abelsche Grippe.