[Haskell-cafe] Need help to solve this question

[Brent Yorgey]

http://www.haskell.org/haskellwiki/Homework_help

On Fri, Mar 11, 2011 at 09:26:59PM +0000, Chatura Roche wrote:
> Both sections relate to the case study: Index for a document of text.
> 
> SECTION A:
> 
> Given the attached Haskell code which produces an index of words, make the
> following alterations by modifying existing functions and including new
> functions where necessary :
> 
> 3) Treat a capitalised word (one or more capitals) as being different from
> the word in all lower case (but they should still be sorted alphabetically)
> – unless it is at the start of a sentence with only the initial letter
> capitalised. A sentence is terminated by a ‘.’, ‘?’ or ‘!’.
> 
> 
> import Prelude
> 
> type Doc = String type Line = String type Word = String
> 
> makeIndex :: Doc -> [ ([Int], Word) ]
> 
> makeIndex
> 
> = shorten . -- [([Int], Word)] -> [([Int], Word)]
> 
> amalgamate .-- [([Int], Word)] -> [([Int], Word)] makeLists . -- [(Int,
> Word)] -> [([Int], Word)] sortLs . -- [(Int, Word)] -> [(Int, Word)]
> 
> allNumWords .-- [(Int, Line)] -> [(Int, Word)] numLines . -- [Line] ->
> [(Int, Line)] splitUp -- Doc -> [Line]
> 
> splitUp :: Doc -> [Line]
> 
> splitUp [] = [] splitUp text
> 
> = takeWhile (/='\n') text : -- first line
> 
> (splitUp . -- splitup other lines
> 
> dropWhile (==’\n’) . -- delete 1st newline(s) dropWhile (/='\n')) text --
> other lines
> 
> numLines :: [Line] -> [(Int, Line)]
> 
> numLines lines -- list of pairs of
> 
> = zip [1 .. length lines] lines -- line no. & line
> 
> -- for each line -- a) split into words -- b) attach line no. to each word
> 
> splitWords :: Line -> [Word] -- a)
> 
> splitWords [] = [] splitWords line
> 
> = takeWhile isLetter line : -- first word in line
> 
> (splitWords . -- split other words
> 
> dropWhile (not.isLetter) . -- delete separators dropWhile isLetter) line --
> other words
> 
> where isLetter ch
> 
> = (‘a’<=ch) && (ch<=’z’)
> 
> (‘A’<=ch) && (ch<=’Z’)
> 
> numWords :: (Int, Line) -> [(Int, Word)] -- b)
> 
> numWords (number, line)
> 
> = map addLineNum ( splitWords line) -- all line pairs
> 
> where addLineNum word = (number, word) -- a pair
> 
> allNumWords :: [(Int, Line)] -> [(Int, Word)]
> 
> allNumWords = concat . map numWords -- doc pairs
> 
> sortLs :: [(Int, Word)] -> [(Int, Word)]
> 
> sortLs [ ] = [ ] sortLs (a:x)
> 
> = sortLs [b | b <- x, compare b a] -- sort 1st half
> 
> ++ [a] ++ -- 1st in middle sortLs [b | b <- x, compare a b] -- sort 2nd half
> 
> where compare (n1, w1) (n2, w2)
> 
> = (w1 < w2) -- 1st word less
> 
> (w1 == w2 && n1 < n2) -- check no.
> 
> makeLists :: [(Int, Word)] -> [([Int], Word)]
> 
> makeLists
> 
> = map mk -- all pairs
> 
> where mk (num, word) = ([num], word)
> 
> -- list of single no.
> 
> amalgamate :: [([Int], Word)] -> [([Int], Word)]
> 
> amalgamate [ ] = [ ] amalgamate [a] = [a] amalgamate ((n1, w1) : (n2, w2) :
> rest)-- pairs of pairs
> 
> | w1 /= w2 = (n1, w1) : amalgamate ((n2, w2) : rest) | otherwise =
> amalgamate ((n1 ++ n2, w1) : rest)
> 
> -- if words are same grow list of numbers
> 
> shorten :: [([Int], Word)] -> [([Int], Word)]
> 
> shorten
> 
> = filter long -- keep pairs >4
> 
> where
> 
> long (num, word) = length word > 4 -- check word >4

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