CSC 372, Spring 2014 Assignment 2 Due: Wednesday, February 26 at 23:00

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1 ASSIGNMENT-WIDE RESTRICTIONS There re two ssignment-wide restrictions: CSC 372, Spring 2014 Assignment 2 Due: Wednesdy, Februry 26 t 23:00 1. The only module you my use is Dt.Chr. 2. Except for problem 1, wrmup.hs, you my not write ny recursive functions! Insted, use higher-order functions like mp, filter, nd foldl. Note tht there is both direct nd indirect recursion. With direct recursion, function f clls itself. With indirect recursion, f might cll g nd then g might cll f. Problem 1. (6 points) wrmup.hs This problem is like wrmup.hs on ssignment 1 I'd like you to write your own version of some functions from the Prelude: mp, filter, foldl, foldr, ny, nd ll. The code for mp, filter, nd foldr re in the slides; the others re esy to find but I'd like you strt with blnk piece of pper nd try to write them from scrtch. If you hve trouble, go hed nd look for the code. Study it but then put it wy nd try to write the function from scrtch. Repet s needed. To void conflicts with the Prelude functions of the sme nme, use these nmes for your versions: Your function mp filt fldl fldr myny myll Prelude function mp filter foldl foldr ny ll You should be ble to write these functions using only pttern mtching, comprisons in gurds, list literls, cons (:), subtrction, nd recursive clls to the function itself. Experiment with the Prelude functions to see how they work. You might find foldl nd foldr to be tough. Don't get stuck on them! This problem, wrmup.hs, is the only problem on this ssignment in which you cn write recursive functions. Pge 1

2 Problem 2. (3 points) dezip.hs Write function dezip list tht seprtes list of 2-tuples into two lists. The first list holds the first element of ech tuple. The second list holds the second element of ech tuple. Don't overlook the problem restrictions following the exmples. > :t dezip dezip :: [(, b)] -> ([], [b]) > dezip [(1,10),(2,20),(3,30)] ([1,2,3],[10,20,30]) > dezip [("just","testing")] (["just"],["testing"]) > dezip [] ([],[]) RESTRICTIONS for dezip.hs: Your solution my only use mp, fst, the composition opertor, nd this function: swp (x,y) = (y,x) Remember tht writing recursive function is prohibited. This function is just like the Prelude function unzip, but with hopefully different enough nme tht you don't test with unzip by mistke! Problem 3. (2 points) repl.hs Write function repl tht works just like replicte in the Prelude. > :t repl repl :: Int -> -> [] > repl 3 7 [7,7,7] > repl 5 '' "" > repl 2 it ["",""] RESTRICTIONS for repl.hs: You my not use replicte. Remember the ssignment-wide prohibition on recursion. This is n esy problem; there re severl wys to solve it using vrious functions from the Prelude. Just for fun you might see how mny distinct solutions you cn come up with. Pge 2

3 Problem 4. (3 points) doubler.hs Crete function nmed doubler tht duplictes ech vlue in list: > :t doubler doubler :: [] -> [] > doubler [1..5] [1,1,2,2,3,3,4,4,5,5] > doubler "bet" "bbeett" > doubler [[]] [[],[]] > doubler [] [] RESTRICTION: Your solution must look like this: doubler = foldr... Tht is, you re to crete doubler using prtil ppliction of foldr. Think bout using n nonymous function. Replce the... with code tht mkes it work. Thirty chrcters should be bout enough but it cn be s long s you need. Problem 5. (2 points) revwords.hs Using point-free style (slide 240), crete function revwords tht reverses the words in sentence. Assume the sentence contins only letters nd spces. > revwords "Reverse the words in this sentence" "esrever eht sdrow ni siht ecnetnes" > revwords "testing" "gnitset" > revwords "" "" Problem 6. (3 points) cpfx.hs is my solution for cpfx from ssignment 1. The cpfx function is recursive. Rewrite tht function to be nonrecursive but still mke use of the cpfx' function. See the ssignment 1 write-up for exmples of using cpfx. Pge 3

4 Problem 7. (10 points) mfilter.hs Write function mfilter tht ccepts list of rnges represented s 2-tuples nd produces function tht when pplied to list of vlues produces the vlues tht do not fll into ny of the rnges. Rnges re inclusive, s the exmples below demonstrte. Note tht mfilter is typed in terms of the Ord type clss, so mfilter works with mny different types of vlues. > :type mfilter mfilter :: Ord => [(, )] -> [] -> [] > mfilter [(3,7)] [1..10] [1,2,8,9,10] > mfilter [(10,18), (2,5), (20,20)] [1..25] [1,6,7,8,9,19,21,22,23,24,25] > mfilter [] [1..3] [1,2,3] > mfilter [('0','9')] "St Feb 8 20:34: " "St Feb :: " > mfilter [('A','Z'), (' ', ' ')] it "teb::" > let f = mfilter [(5,20),(-100,0)] > f [1..30] [1,2,3,4,21,22,23,24,25,26,27,28,29,30] > f [-10,-9..21] [1,2,3,4,21] Assume for rnge (x, y) tht x <= y, i.e, you won't see rnge like (10,1) or ('z', ''). As you cn see bove, rnges re inclusive. A rnge like (1,3) blocks 1, 2, nd 3. Just for fun...here's n instnce declrtion from the Prelude: instnce (Ord, Ord b) => Ord (, b) It sys tht if the vlues in 2-tuple re orderble, then the 2-tuple is orderble. With tht in mind, consider this mfilter exmple: > mfilter [((3,'z'),(25,''))] (zip [1..] [''..'z']) [(1,''),(2,'b'),(3,'c'),(25,'y'),(26,'z')] Remember: No explicit recursion! NOTE: This problem requires somewht cretive lep. I won't sy more bout tht here so I don't spoil it for nybody but don't feel bd bout sking for hint on this one. Pge 4

5 Problem 8. (10 points) nnn.hs The behvior of the function you re to write for this problem is best shown with n exmple: > nnn [3,1,5] ["3-3-3","1"," "] The first element is 3 nd tht cuses corresponding vlue in the result to be string of three 3s, seprted by dshes. Then we hve one 1. Then five 5s. More exmples: > :t nnn nnn :: [Int] -> [[Chr]] > nnn [1,3..10] ["1","3-3-3"," "," "," "] > nnn [10,2,4] [" ","2-2"," "] > length (hed (nnn [100])) 399 Note the mth for the lst exmple: 100 copies of "100" nd 99 copies of "-" to seprte them. Assume tht the vlues re greter thn zero. Remember: No explicit recursion! Problem 9. (10 points) expnd.hs Consider the following two entries tht specify the spelling of word nd spelling of forms of the word with suffixes: progrm,s,#ed,#ing,'s code,s,d,@ing If suffix begins with pound sign (#), it indictes tht the lst letter of the word should be doubled when dding the suffix. If suffix begins with t-sign (@), it indictes tht the lst letter of the word should be dropped when dding the suffix. In other cses, including the possessive ('s), the suffix is simply dded. The bove two entries represent the following words: progrm progrms progrmmed progrmming progrm's code codes coded coding Pge 5

6 For this problem you re to write function expnd entry tht returns list tht begins with the word with no suffix nd followed by ll the suffixed forms in turn. > :t expnd expnd :: [Chr] -> [String] > expnd ["code","codes","coded","coding"] > expnd "progrm,s,#ed,#ing,'s" ["progrm","progrms","progrmmed","progrmming","progrm's"] > expnd "drift" (If no suffixes, produce just the word.) ["drift"] > expnd ",b,c,d,e,f" ["","b","c","d","e","f"] > expnd ["","b","c","d","x","y","z","1","2","3"] > expnd ["b","bbc","bd","e","bf","b::x"] A word my hve ny number of suffixes with n rbitrry combintion of types. Words nd suffixes my be rbitrrily long. The only chrcters with specil mening re comm, #, Everything is just text. Assume tht the entry is well-formed. You won't see things like zero-length word or suffix. Here re some exmples of entries we will not test with: ",", "test,", "test,s,#,@" Remember: No explicit recursion! Problem 10. (18 points) pnckes.hs In this problem you re to print representtion of series of stcks of pnckes. Let's strt with n exmple: > :t pnckes pnckes :: [[Int]] -> IO () > pnckes [[3,1],[3,1,5]] *** *** * * ***** > The list specifies two stcks of pnckes: the first stck hs two pnckes, of widths 3 nd 1, respectively. The second stck hs three pnckes. Pnckes re lwys centered on their stck. A single spce seprtes ech stck. Pnckes re lwys represented with sterisks. Pge 6

7 Here's nother exmple: > pnckes [[1,5],[1,1,1],[11,3,15],[3,3,3,3],[1]] *** * *********** *** * * *** *** ***** * *************** *** * > There re opportunities for cretive cooking: > pnckes [[7,1,1,1,1,1],[5,7,7,7,7,5],[7,5,3,1,1,1], [5,7,7,7,7,5], [7,1,1,1,1,1],[1,3,3,5,5,7]] ******* ***** ******* ***** ******* * * ******* ***** ******* * *** * ******* *** ******* * *** * ******* * ******* * ***** * ******* * ******* * ***** * ***** * ***** * ******* > Assume tht there is t lest one stck. Assume ll stcks hve t lest one pncke. Assume ll widths re greter thn zero. The smllest order you'll see is this: > pnckes [[1]] * > To void problems with centering, ssume ll pncke widths re odd. Like street on ssignment 1, pnckes produces output. (Now we know to sy tht street nd pnckes re functions tht produce ctions see slide 276 nd following.) My solution is structured like this: pnckes stcks = putstr result where... result =... Remember: No explicit recursion! Problem 11. (18 points) group.hs For this problem you re to write progrm tht reds text file nd prints the file with line of dshes inserted whenever the first chrcter on line differs from the first chrcter on the previous line. Additionlly, the lines from the input file re to be numbered. % ct group.1 ble cdemi lge crton firwy hex hockshop Pge 7

8 % runghc group.hs group.1 1 ble 2 cdemi 3 lge 4 crton 5 firwy 6 hex 7 hockshop % Note tht only the lines from the input file re numbed the seprtors re not numbered. Lines with length of zero (i.e., length line == 0) re discrded s first step. Another exmple: % ct group.2 elempos' _ [] = -1 elempos' x ((vl,pos):vps) x == vl = pos otherwise = elempos' x vps f x y z = (x == chr y) == z dd_c x y = x + y dd_t(x,y) = x + y fromtomn 'I' = 1 fromromn 'V' = 5 fromromn 'X' = 10 p 1 (x:xs) = 10 % runghc group.hs group.2 1 elempos' _ [] = -1 2 elempos' x ((vl,pos):vps) 3 x == vl = pos 4 otherwise = elempos' x vps 5 f x y z = (x == chr y) == z 6 dd_c x y = x + y 7 dd_t(x,y) = x + y 8 fromtomn 'I' = 1 9 fromromn 'V' = 5 10 fromromn 'X' = p 1 (x:xs) = 10 % Pge 8

9 Note tht when the line numbers grow to two digits the line contents re shifted column to the right. Tht's ok. If ll lines strt with the sme chrcter, no seprtors re printed. % ct group.3 test tests testing % runghc group.hs group.3 1 test 2 tests 3 testing % One finl exmple: % ct group.4 b b b b % runghc group.hs group b 3 4 b b b % The seprtor lines re six dshes (minus signs). Assume tht there is t lest one line in the input file. (A one-line file will produce no seprtors, of course.) hs the group.[1234] Pge 9

10 files shown bove. (Tht's /cs/www/clsses/cs372/spring14/2 if you're on lectur.) Implementtion note: Unlike everything else you've done with Hskell, this is whole progrm, not just function run t the ghci prompt. Follow the exmple of longest on slides nd hve binding for min tht hs do block tht sequences getting the commnd line rguments with getargs, reding the whole file with redfile, nd then clling putstr with result of function nmed group, which does ll the computtion. Your group.hs might look like this: import System.Environment (getargs) min = do rgs <- getargs bytes <- redfile (hed rgs) putstr (group bytes)...your functions here... Note tht to run group.hs, you use runghc on the commnd line. If you've instlled The Hskell Pltform for Windows using the defults, I believe you'll find tht you hve runghc commnd t your disposl. Here's wht running it t Windows XP commnd prompt looks like: W:\372>runghc group.hs group.1 1 ble 2 cdemi 3 lge 4 crton 5 firwy 6 hex 7 hockshop W:\372> Note tht the blnk line following "7 hockshop" is produced by Windows, not group. If you're working on your own mchine I recommend tht you do simple test of runghc ASAP, so tht if problems turn up, we'll hve plenty of time to help you get it working. Just try version check: W:\372>runghc --version runghc Remember: No explicit recursion! Problem 12. Extr Credit observtions.txt Submit plin text file nmed observtions.txt with... () (1 point extr credit) An estimte of how long it took you to complete this ssignment. To fcilitte progrmmtic extrction of the hours from ll submissions hve n estimte of hours on line by itself, Pge 10

11 more or less like one of these: Hours: 10 Hours: Hours: 15+ Other comments bout the ssignment re welcome, too. Ws it too long, too hrd, too detiled? Spek up! I pprecite ll feedbck, fvorble or not. (b) (1-3 points extr credit) Cite n interesting course-relted observtion (or observtions) tht you mde while working on the ssignment. The observtion should hve t lest little bit of depth. Think of me sying "Good!" s one point, "Interesting!" s two points, nd "Wow!" s three points. I'm looking for qulity, not quntity. Turning in your work Use the D2L Dropbox nmed 2 to submit single zip file nmed 2.zip tht contins ll your work. If you submit more thn one 2.zip, we'll grde your finl submission. Here's the full list of deliverbles: wrmup.hs dezip.hs repl.hs doubler.hs revwords.hs cpfx.hs mfilter.hs nnn.hs expnd.hs pnckes.hs group.hs observtions.txt (for extr credit) DO NOT SUBMIT INDIVIDUAL FILES submit file nmed 2.zip tht contins ech of the bove files. Note tht ll chrcters in the file nmes re lowercse. Hve ll the deliverbles in the uppermost level of the zip. It's ok if your zip includes other files, too. Miscellneous This ssignment is bsed on the mteril on Hskell slides Point vlues of problems correspond directly to ssignment points in the syllbus. For exmple, 10-point problem on this ssignment corresponds to 1% of your finl grde in the course. Feel free to use comments to document your code s you see fit, but note tht no comments re required, nd no points will be wrded for documenttion itself. (In other words, no prt of your score will be bsed on documenttion.) Two minus signs (--) is comment to end of line; {- nd -} re used to enclose block comments, like /* nd */ in Jv. Remember tht lte ssignments re not ccepted nd tht there re no lte dys; but if circumstnces Pge 11

12 beyond your control interfere with your work on this ssignment, there my be grounds for n extension. See the syllbus for detils. My estimte is tht it will tke typicl CS junior from 10 to 15 hours to complete this ssignment. Keep in mind the point vlue of ech problem; don't invest n inordinte mount of time in problem or become incredibly frustrted before you sk for hint or help. Remember tht the purpose of the ssignments is to build understnding of the course mteril by pplying it to solve problems. If you rech the eight-hour mrk, regrdless of whether you hve specific questions, it's probbly time to touch bse with us. Give us chnce to speed you up! Our gol is tht everybody gets 100% on this ssignment AND gets it done in n mount of time tht is resonble for them. When developing code tht performs complex series of trnsformtions on dt I recommend the technique shown for longest, strting on slide 226. Tht is, work through series of lets to check the trnsformtion mde by ech step. I hte to hve to mention it but keep in mind tht cheters don't get second chnce. If you give your code to somebody else nd they turn it in, you'll both likely fil the clss, nd more. (See the syllbus for the detils.) REMEMBER: Except for wrmup.hs you re not permitted to write ny recursive functions on this ssignment! Pge 12