1. (34 points) Suppose that the following definitions are made: (a) (22 points) Give the values of the following expressions.

Transcription

1 1. (34 points) Suppose that the following definitions are made: import Data.Char ice :: [(Char,Integer)] ice = [( d,12), ( m,3), ( j,5),( f,2)] curl :: [a] -> String curl [] = "skip" curl (x:z) = "vice" curl (w:y:ts) = "lead" sweep :: a -> (Float,a) sweep x = (1.0,x) freeze :: Integer -> [(Char,Integer)] -> String freeze i [] = [] freeze i ((w,p):rest) i == p = w : freeze i rest otherwise = "!!" hurry :: Int -> Bool hurry v = v > 100 even v (a) (22 points) Give the values of the following expressions. (i). 3:5:1:[] [3,5,1] (ii). div (iii). curl [1,10,100] "vice" (iv). hurry 18 True (v). [20,24..30] [20,24,28] (vi). isupper? False (vii). length [[2,4],[7],[],[8,6]] 4 (viii). [ r (r,m) <- ice, odd m] "mj" (ix). freeze 12 ice "d!!" (x). zip [3,6,10,12] [20,30,40] [(3,20),(6,30),(10,40)] (xi). concat [[2,7],[],[31,8,2]] [2,7,31,8,2] (b) (12 points) Give the types of the following expressions (e.g., the type of [False] is [Bool]).

2 (i). ["104","days"]:[] [[String]] (ii). (odd 6, length [3.5]) (Bool,Int) (iii). unzip ice ([Char],[Integer]) (iv). sweep Q (Float,Char) (v). fst (hurry 13,"sun") Bool (vi). [ sweep b (a,b) <- ice] [(Float,Integer)] 2. (16 points) Consider the following (partial) file system hierarchy, where the numeric labels associated with directories are intended merely as identification for the questions that follow: 1 / 2 dei/ 8 missions/ 9 owca/ 3 doof/ 4 norm/ 10 carl/ 11 mm/ 12 perry/ 13 silentg/ 5 backstory/ 6 inators/ 7 plans/ 14 family/ 15 gear/ 16 missions/ 17 plans/ For each question that follows, suppose that Perry s home directory is directory #12 and that his current working directory is directory #6. (a) If Perry executed the Unix command pwd, what would be the system s response? /dei/doof/inators (b) If Perry executed the Unix command cd.., which directory would become his current working directory? (Give the number of the directory, not the name.) #3 (c) If Perry executed the Unix command cd ~/.., which directory would become his current working directory? (Give the number of the directory, not the name.) #9

3 As before, suppose that Perry s home directory is directory #12 and that his current working directory is directory #6. For each of the following tasks, give a single Unix command would allow Perry to complete the task. You should assume that each task is completed independently of the others (i.e., changes made in one task do not affect other tasks). (d) List all files (including hidden files) in directory #7, but do not include info about file permissions and creation dates ls -a../plans (e) Create a subdirectory in directory #8 called canada mkdir /missions/canada (f) Make a copy of the file watch.pdf (located in directory #10), placing it in directory #15 with the name new.pdf cp /owca/carl/watch.pdf ~/gear/new.pdf (g) Delete the file vacation (located in directory #17) rm ~/plans/vacation (h) Move the file seattle (located in directory #16) to directory #13 mv ~/missions/seattle /owca/silentg 3. (16 points) A small burger shop sells burgers and fries (and not much else): The standard cost for a burger is $7, and the cost for an order of fries is $2. To attract new customers, the shop is currently running a promotion: for every two burgers purchased at the standard price, one order of fries is free. The shop also has a loyalty program for repeat customers. Customers who present their membership card at the time of purchase pay only $6 per burger (but they pay full price for all fries). Here are examples of how the pricing works: Ana wishes to purchase five burgers and three orders of fries. She does not present a membership card at the time of purchase. Because she s ordering five burgers, she is eligible for two free orders of fries. She therefore pays a total of $37 (five burgers at $7 apiece, plus $2 for the one non-free order of fries). Blake also wishes to purchase five burgers and three orders of fries, but he does present his membership card at the time of purchase. Because he s using his membership card, he is not eligible for any free orders of fries. He pays a total of $36 (five burgers at $6 apiece, plus three orders of fries at $2 apiece). Cora wishes to purchase three burgers and no fries, and she does not present a membership card at the time of purchase. Because she s ordering three burgers, she would be eligible for one free order of fries, but she doesn t use that benefit. She pays a total of $21 (three burgers at $7 apiece). Your task: Write a Haskell function

4 cost :: Integer -> Integer -> Bool -> Integer such that cost burgs fries card calculates the cost (in dollars) of a customer s food purchase, where burgs indicates the number of burgers purchased, fries indicates the number of orders of fries desired, and card is true precisely when the customer presents a membership card at the time of purchase. If either burgs or fries is negative, the function should return 0. For example, your function should have the following behavior: *Main> cost 5 3 False 37 *Main> cost 5 3 True 36 *Main> cost 3 0 False 21 *Main> cost 3 0 True 18 cost burgs fries card burgs < 0 fries < 0 = 0 card = burgs * 6 + fries * 2 otherwise = burgs * 7 + paidfries * 2 where paidfries = max 0 (fries - div burgs 2) cost card burgs fries burgs < 0 fries < 0 = 0 card = burgs * 6 + fries * 2 paidfries > 0 = burgs * 7 + paidfries * 2 otherwise = burgs * 7 where paidfries = fries - div burgs 2 4. (10 points) Write a Haskell function neighbors :: [a] -> [(a,a)] such that neighbors xs returns a list of all pairs of neighboring (i.e., adjacent) elements of xs. For example, the function should have the following behavior: *Main> neighbors [3,0,21,3,3,7,1] [(3,0),(0,21),(21,3),(3,3),(3,7),(7,1)] *Main> neighbors "cis252" [( c, i ),( i, s ),( s, 2 ),( 2, 5 ),( 5, 2 )] *Main> neighbors [3] [] neighbors (x:y:zs) = (x,y) : neighbors (y:zs) neighbors zs = [] -- handles [] and singletons

5 neighbors [] = [] neighbors (x:xs) = zip (x:xs) xs 5. (12 points) Write a Haskell function changefirst :: Char -> String -> String such that changefirst ch cs returns the string obtained by changing the first occurrence of ch in cs to # (everything else in the string stays the same). For example: *Main> changefirst 2 "cis 252" "cis #52" *Main> changefirst A "cis 252" "cis 252" Sample solution: changefirst ch [] = [] changefirst ch (c:cs) ch == c = # :cs otherwise = c: changefirst ch cs 6. (12 points) Write a Haskell function addsome :: Int -> [(Int,Char)] -> Int such that addsome k ps calculates the sum of the first k numbers paired with a lowercase letter in the list ps. (If there are fewer than k pairs with lowercase letters, then the function sums those that exist; when k is nonpositive, the function returns 0.) For example, the list [(5,! ),(3, b ),(6, w ),(8, Q ),(12, $ ),(-1, s ),(6, b )] has four numbers paired with lowercase letters: 3, 6, -1, and 6. Thus, addsome has the following behavior: *Main> addsome 1 [(5,! ),(3, b ),(6, w ),(8, Q ),(12, $ ),(-1, s ),(6, b )] 3 *Main> addsome 2 [(5,! ),(3, b ),(6, w ),(8, Q ),(12, $ ),(-1, s ),(6, b )] 9 *Main> addsome 3 [(5,! ),(3, b ),(6, w ),(8, Q ),(12, $ ),(-1, s ),(6, b )] 8 *Main> addsome 10 [(5,! ),(3, b ),(6, w ),(8, Q ),(12, $ ),(-1, s ),(6, b )] 14 *Main> addsome (-2) [(5,! ),(3, b ),(6, w ),(8, Q ),(12, $ ),(-1, s ),(6, b )] 0 addsome k [] = 0 addsome k ((m,c):rest) k <= 0 = 0 islower c = m + addsome (k-1) rest otherwise = addsome k rest addsome k ps = sum (take k [m (m,c) <- ps, islower c])