18.hs

compileNewList :: [Int] -> [Int] -> [Int]
compileNewList lowerLayer [a] = [largestSum a (head lowerLayer) (head (tail lowerLayer))]
compileNewList lowerLayer upperLayer = (largestSum (head upperLayer) (head lowerLayer) (head (tail lowerLayer))) : compileNewList (tail lowerLayer) (tail upperLayer)

largestSum :: Int -> Int -> Int -> Int
largestSum upperLayer lowerLayer1 lowerLayer2 = if lowerLayer2 > lowerLayer1 then upperLayer + lowerLayer2 else upperLayer + lowerLayer1 

loop :: [[Int]] -> Int
loop [a,b] = largestSum (head a) (head b) (head (tail b))
loop array = loop ((take (arrayLength-2) array) ++ [compileNewList (array !! (arrayLength-1)) (array !! (arrayLength-2))])
    where 
        arrayLength = length array

main = print $ loop [[75],[95,64],[17,47,82],[18,35,87,10],[20,04,82,47,65],[19,01,23,75,03,34],[88,02,77,73,07,63,67],[99,65,04,28,06,16,70,92],[41,41,26,56,83,40,80,70,33],[41,48,72,33,47,32,37,16,94,29],[53,71,44,65,25,43,91,52,97,51,14],[70,11,33,28,77,73,17,78,39,68,17,57],[91,71,52,38,17,14,91,43,58,50,27,29,48],[63,66,04,68,89,53,67,30,73,16,69,87,40,31],[04,62,98,27,23,09,70,98,73,93,38,53,60,04,23]]