On 8/15/07, Alexteslin
I am really sorry, but i still can't define the function. The chapter the exercise is in precedes algebraic types or Maybe a types. And is seems that must being easy to define. I answered some exercises on using foldr such as summing for example, but this one i am trying:
myLast :: [Int] -> Int myLast (x:xs) = foldr (some function) x xs.
With summing as i understood foldr goes through the list and sums up by (+) operator and one argument like 0. Like: foldr (+) 0 xs
I don't think you can do it directly using just foldr. However, you can use foldr to build up a function that, when applied to the list, will evaluate to the last element. foldr will be acting like a function composition engine that evaluates to a function to process the list. I got the idea for this from the article titled "Getting a Fix from the Right Fold" in The Monad Read Issue 6 (http://www.haskell.org/sitewiki/images/1/14/TMR-Issue6.pdf). See if reading that article helps. In particular, Solution 2 described in the article is the one with the structure I'm talking about. (Solution 3 fixes a space leak in Solution 2, if you want a bit more complexity.)