CIS 252 Introduction to Computer Science Section M013: Exam 2 (Green) March 29, Points Possible

Transcription

1 Name: CIS 252 Introduction to Computer Science Section M013: March 29, 2018 Question Points Possible Points Received Total 100 Instructions: 1. This exam is a closed-book (and closed-notes) exam. 2. Legibility counts! Make sure we can read (and find!) your answers. If you need more room for an answer than that given, use the back side of the pages. Be sure to leave a note indicating where the answer is. 3. This test should have 7 pages (including this cover sheet). Let us know now if your copy does not have the correct number of pages. 4. Unless specified otherwise, you may use any built-in Haskell function you want, as long as you use it correctly (including using its correct name). The last page includes a list of some common Haskell functions and their types.

2 1. (18 points) Suppose that the following definitions are made: import Data.Char data Field = Pasture Char Lawn Integer Float Meadow String [Integer] gaze :: Integer -> Bool gaze m = odd m && m < 10 wonder :: (Char -> Bool) -> String -> Float wonder h (c:cs) h c = 6.0 otherwise = wonder h cs wonder h [] = plow :: Field -> Integer plow (Lawn s t) = s plow (Meadow cs (d:e:rest)) = e + plow (Pasture G ) plow _ = 70 Give the values of the following expressions. (a) (\ m -> [m+20]) 5 (b) [3,5..12] (c) unzip [(2,3),(9,1),(6,8)] (d) map gaze [6,3,7,11,2] (e) [2,9,3]:[] (f) plow (Lawn ) (g) plow (Meadow "tractor" [5,9,2]) (h) takewhile even [4,2,1,8,6,7,3] (i) wonder islower "SYRacUsE"

3 2. (18 points) Suppose that the following definitions are made (same as in Question 1): import Data.Char data Field = Pasture Char Lawn Integer Float Meadow String [Integer] gaze :: Integer -> Bool gaze m = odd m && m < 10 wonder :: (Char -> Bool) -> String -> Float wonder h (c:cs) h c = 6.0 otherwise = wonder h cs wonder h [] = plow :: Field -> Integer plow (Lawn s t) = s plow (Meadow cs (d:e:rest)) = e + plow (Pasture G ) plow _ = 70 Give the types of the following expressions. (a) fst (plow,gaze) (b) Pasture e (c) (\ (w,z) -> w + length z) (d) [ gaze k k <- [1..4] ] (e) filter isalpha [] (f) Meadow (g) uncurry (&&) (h) zip "code" (i) [toupper, tolower]

4 3. (12 points) For each of the following, fill in the blank with a pattern that gives the function the indicated behavior. (a) one "apple" should return a and one [3,1,4,1,5,9] should return 3: one = r (b) two [6,4,2,3,5] should return [2,4] and two "spring" should return "rp": two = [a,b] (c) three (3, g,7) should return 4, and three ( m,true,5) should return 2: three = c-3 (d) four [(10,20),(30,40)] should return 40, and four [(5,6),(7,8),(9,0)] should return 8: four = d 4. (6 points) Consider the following Haskell function: quibble :: Int -> [(Char,Int)] -> [Int] quibble j ps = [ m-j (d,m) <- ps, isalpha d ] Fill in the blanks below to write an equivalent function using map and filter: quibble j ps = map (filter ps)

5 5. (34 points) A small burrito shop offers a very limited menu: Drinks are available for $3.00 each. A large order of nachos costs $12.95, and a small order of nachos costs $8.50. There are three styles of burritos: chicken burritos, shrimp burritos, and bean burritos. The bean burritos costs $9.25 apiece; all other burritos cost $11.00 each. There are four fillings that can be added to burritos in any combination and any amount: rice, cheese, salsa, and onions. Each unit of filling adds $0.50 to the cost of a burrito, so (for example) adding two units of salsa and one unit of cheese increases a burrito s cost by $1.50. These menu options can be represented with the following Haskell types (note that none of the types belong to the Eq class, so you cannot use == or /= on values of these types): data Style = Chicken Shrimp Bean data Filling = Rice Cheese Salsa Onions data Size = Small Large data MenuItem = Drink Nachos Size Burrito Style [Filling] (a) (15 points) Write a Haskell function price :: MenuItem -> Float such that price item calculates the price (in dollars) of item. For example: *Main> price (Nachos Large) *Main> price (Burrito Bean [Rice, Onions, Rice, Cheese]) *Main> price (Burrito Shrimp []) 11.0

6 (b) (12 points) Write a Haskell function cutcalories :: MenuItem -> MenuItem such that cutcalories item returns a menu item that is similar to item except that (i) large orders are replaced by small orders and (ii) any cheese is removed. For example: *Main> cutcalories (Nachos Large) Nachos Small *Main> cutcalories (Burrito Shrimp [Rice,Cheese,Salsa,Onions,Cheese]) Burrito Shrimp [Rice,Salsa,Onions] *Main> cutcalories Drink Drink (c) (7 points) Write a Haskell function withrice :: [MenuItem] -> Int such that withrice items computes the number of burritos in items that contain Rice. For example: *Main> withrice [Burrito Bean [Rice, Salsa, Rice], Burrito Shrimp []] 1 *Main> withrice [Drink, Nachos Small, Burrito Bean [Cheese]] 0

7 6. (12 points) Write a Haskell function changefirst :: (a -> Bool) -> a -> [a] -> [a] such that changefirst p val xs returns a list that looks like xs except that the leftmost item in xs that satisfies predicate p is replaced by val. (If none of the elements of xs satisfy p, then xs is returned.) For example: *Main> changefirst even 33 [1,7,4,8,2] [1,7,33,8,2] *Main> changefirst even 33 [1,7,9,5] [1,7,9,5] *Main> changefirst islower! "Syracuse" "S!racuse" Types of some standard Haskell functions (:) :: a -> [a] -> [a] (++) :: [a] -> [a] -> [a] (&&), ( ) :: Bool -> Bool -> Bool sum, product :: Num a => [a] -> a even, odd :: Integral a => a -> Bool length :: [a] -> Int isalpha, isupper, islower :: Char -> Bool toupper, tolower :: Char -> Char fst :: (a,b) -> a snd :: (a,b) -> b zip :: [a] -> [b] -> [(a,b)] unzip :: [(a,b)] -> ([a],[b]) map :: (a -> b) -> [a] -> [b] filter :: (a -> Bool) -> [a] -> [a] takewhile, dropwhile :: (a -> Bool) -> [a] -> [a] uncurry :: (a -> b -> c) -> (a,b) -> c curry :: ((a,b) -> c) -> a -> b -> c