[Haskell-cafe] Re: defining last using foldr

Kurt Hutchinson wrote:

On 8/15/07, Alexteslin wrote:

...

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.

Something like this? (spoiler warning) http://hpaste.org/2283