p1
halveEvens :: [Int] -> [Int]
halveEvens xs = [x `div` 2  | x<-xs, even x ]

p2
halveEvensRec :: [Int] -> [Int]
halveEvensRec [] = []
halveEvensRec (x:xs) | even x      = div x 2 : halveEvensRec (xs)
                     | otherwise = halveEvensRec(xs)

p3
inRange :: Int ->  Int -> [Int] -> [Int]
inRange lo hi xs = [ x| x<-xs,x>=lo, x<=hi]

p4
inRangeRec :: Int ->  Int -> [Int] -> [Int]
inRangeRec lo hi [] = []
inRangeRec lo hi (x:xs) | x<=hi && x>= lo = x : inRangeRec lo hi xs
						            | otherwise		   = inRangeRec lo hi xs

p5
countPositives :: [Int] -> Int
countPositives xs = length [ x | x<- xs, x>0 ]

p6
countPositivesRec :: [Int] -> Int
countPositivesRec [] = length []
countPositivesRec (x:xs) | x<=0 		 = countPositivesRec(xs)
						 | otherwise = length[x] + countPositivesRec(xs)
p6'
countPositivesRec :: [Int] -> Int
countPositivesRec [] = 0
countPositivesRec (x:xs) = (if x<=0 then 0 else 1) + countPositivesRec(xs)

p7.//copied from solution                                                                 // BEWARE OF COPYING
-- Helper function
discount :: Int -> Int
discount price = round(0.9 * fromIntegral price)

-- List-comprehension version of pennypincher
pennypincher :: [Int] -> Int
pennypincher prices = sum [discount price |price <- prices, discount price <=19900 ]

p8
-- Helper function
discount :: Int -> Int
discount price = round(0.9 * fromIntegral price)

-- Recursive version
pennypincherRec :: [Int] -> Int
pennypincherRec [] = 0
pennypincherRec (price:prices) =(if discount price <=19900 then discount price else 0) + pennypincherRec(prices)


p9
multDigits :: String -> Int
multDigits str = product[ (if isDigit(x) then digitToInt(x) else 1) | x<-str]
p9'                                                          smart definition using ord[which tells the ascii no of a particular item]
multDigits cs = product [ ord c - ord '0' | c <- cs, isDigit c]                       like ord '0' = 48


p10
multDigitsRec :: String -> Int
multDigitsRec [] = 1
multDigitsRec (x:xs) = (if isDigit x then ord x - ord '0' else 1) * multDigitsRec(xs)

p10'
multDigitsRec :: String -> Int
multDigitsRec [] = 1
multDigitsRec (x:xs) | isDigit x = digitToInt x * multDigitsRec xs
					           | otherwise = 1 * multDigitsRec xs



p11
capitalise :: String -> String
capitalise ""     = ""
capitalise (x:xs) = toUpper x : [toLower x' | x'<-xs ]


p12
-- Recursive version
capitaliseRec :: String -> String
capitaliseRec [] = ""
capitaliseRec (x:xs) = toUpper x : lowerRec xs

-- Helper function
lowerRec :: String -> String
lowerRec [] = ""
lowerRec (x:xs) = toLower x : lowerRec xs