Question

All of the problems must be done in Haskell. You may download a local IDE or use [this website.][https://repl.it/languages/haskell].

You are not allowed any functions that trivialize a problem!

Here are some examples of lists you can test your solutions on: let list1 = [5, 10, 15, 20, 25, 30]

let list2 = [50, 100, 150, 200, 250, 300]

1. Write a function that returns the maximum value in a list.
2. Write a function that returns the nth element in the list.
3. Write a function that doubles the values in a list.
4. Write function that accepts an integer and a list. It should return 1 if the integer is in the list, and -1 if it is not.
5. Write a function that combines two lists into a list of tuples.

Answer 1

1  Write a function that returns the maximum value in a list.

findMax :: [Int] -> Maybe Int findMax [] = Nothing findMax (x:xs) = case (findMax xs) of Nothing -> Just x Just m -> if x > m then Just x else Just m main = print $ show $ findMax [5,10,15,20,25,30]

2. Write a function that returns the nth element in the list.

primes = 2 : sieve [5,10,15,20,25,30] where

sieve [] = []

sieve (p:xs) = p : sieve (xs `minus` [p,p+2*p..

*Main> :t (!!) (!!) :: [a] -> Int -> a

3. Write a function that doubles the values in a list

duplicateEach = (>>= replicate 2) duplicateEach2 = concatMap (replicate 2) duplicateEach3 xs = [ y | x <- xs, y<-[x,x] ] 

4. Write a function that combines two lists into a list of tuples.

zipThree :: [a] -> [b] -> [c] -> Maybe [(a, b, c)] zipThree [] [] [] = Just [] zipThree (x:xs) (y:ys) (z:zs) = case zipThree xs ys zs of Nothing -> Nothing Just as -> Just $ (x, y, z) : as zipThree _ _ _ = Nothing