On Fri, Sep 25, 2015 at 06:18:08PM -0500, jamb@hinojosa.com wrote:
Hello,
I am a complete Haskell beginner and I am doing some exercises of my book but I am stuck with the following:
Define myMax :: Ord a => [a] -> a which returns the maximum element of a list.
I must use foldl1 or foldr1 and I am given the hint to use max which gets the maximum of 2 elements.
I will very much appreciate if you help me solve it.
Let's say you have foldl1 f [1,7,2,5] where f is a binary operator (a function that 'takes two parameters'). `foldl1` will apply 1 and 7 to f, obtaining X, so we have: X and [2,5] then it will apply X and 2 to f, obtaining Y, so we're left with Y and 5 and finally `f Y 5`, leading to your final result Z. Now, if `f a b = a + b`, we would have [1,7,2,5] -- 1+7 8 [2,5] -- 8+2 10 [5] -- 10+5 15 <-- final result But you aren't interested in the sum of the list, but its maximum. Which operation could you use instead of (+) to achieve your goal?