diff --git a/src/Chapter1.hs b/src/Chapter1.hs index 04fed0db..d06354be 100644 --- a/src/Chapter1.hs +++ b/src/Chapter1.hs @@ -209,31 +209,31 @@ So, the output in this example means that 'False' has type 'Bool'. > Try to guess first and then compare your expectations with GHCi output >>> :t True - +True :: Bool >>> :t 'a' - +'a' :: Char >>> :t 42 - +42 :: Num p => p A pair of boolean and char: >>> :t (True, 'x') - +(True,'x') :: (Bool, Char) Boolean negation: >>> :t not - +not :: Bool -> Bool Boolean 'and' operator: >>> :t (&&) - +(&&) :: Bool -> Bool -> Bool Addition of two numbers: >>> :t (+) - +(+) :: Num a => a -> a -> a Maximum of two values: >>> :t max - +max :: Ord a => a -> a -> a You might not understand each type at this moment, but don't worry! You've only started your Haskell journey. Types will become your friends soon. @@ -301,43 +301,43 @@ expressions in GHCi functions and operators first. Remember this from the previous task? ;) >>> 1 + 2 - +3 >>> 10 - 15 - +-5 >>> 10 - (-5) -- negative constants require () - +15 >>> (3 + 5) < 10 - +True >>> True && False - +False >>> 10 < 20 || 20 < 5 - +True >>> 2 ^ 10 -- power - +1024 >>> not False - +True >>> div 20 3 -- integral division - +6 >>> mod 20 3 -- integral division remainder - +2 >>> max 4 10 - +10 >>> min 5 (max 1 2) - +2 >>> max (min 1 10) (min 5 7) - +5 Because Haskell is a __statically-typed__ language, you see an error each time you try to mix values of different types in situations where you are not @@ -428,7 +428,7 @@ task is to specify the type of this function. >>> squareSum 3 4 49 -} - +squareSum :: Int -> Int -> Int squareSum x y = (x + y) * (x + y) @@ -448,8 +448,8 @@ Implement the function that takes an integer value and returns the next 'Int'. every type ｡.☆.*｡. No need to worry much about "error" here, just replace the function body with the proper implementation. -} -next :: Int -> Int -next x = error "next: not implemented!" +next :: Integer->Integer +next x = x + 1 {- | After you've implemented the function (or even during the implementation), you @@ -489,8 +489,9 @@ Implement a function that returns the last digit of a given number. results. Or you can try to guess the function name, search for it and check whether it works for you! -} --- DON'T FORGET TO SPECIFY THE TYPE IN HERE -lastDigit n = error "lastDigit: Not implemented!" +lastDigit :: Int->Int +lastDigit n = mod (abs n) 10 + {- | @@ -520,7 +521,7 @@ branches because it is an expression and it must always return some value. satisfying the check will be returned and, therefore, evaluated. -} closestToZero :: Int -> Int -> Int -closestToZero x y = error "closestToZero: not implemented!" +closestToZero x y = if abs x < abs y then x else y {- | @@ -553,8 +554,11 @@ value after "=" where the condition is true. Casual reminder about adding top-level type signatures for all functions :) -} - -mid x y z = error "mid: not implemented!" +mid :: Int -> Int -> Int -> Int +mid x y z + | x>y && x>z = if y>z then y else z + | y>z = if x>z then x else z + | otherwise = if x>y then x else y {- | =⚔️= Task 8 @@ -568,7 +572,14 @@ True >>> isVowel 'x' False -} -isVowel c = error "isVowel: not implemented!" +isVowel :: Char->Bool +isVowel c + | c == 'a' = True + | c == 'e' = True + | c == 'i' = True + | c == 'o' = True + | c == 'u' = True + | otherwise = False {- | @@ -631,8 +642,11 @@ Implement a function that returns the sum of the last two digits of a number. Try to introduce variables in this task (either with let-in or where) to avoid specifying complex expressions. -} - -sumLast2 n = error "sumLast2: Not implemented!" +sumLast2 :: Int->Int +sumLast2 n = + let (x,last) = divMod (abs n) 10 + last2 = mod x 10 + in (last+last2) {- | @@ -652,8 +666,8 @@ Implement a function that returns the first digit of a given number. You need to use recursion in this task. Feel free to return to it later, if you aren't ready for this boss yet! -} - -firstDigit n = error "firstDigit: Not implemented!" +firstDigit :: Int -> Int +firstDigit n = if abs n<10 then abs n else firstDigit(div n 10) {- diff --git a/src/Chapter2.hs b/src/Chapter2.hs index f7c02ce2..54c1e78e 100644 --- a/src/Chapter2.hs +++ b/src/Chapter2.hs @@ -136,43 +136,43 @@ functions in GHCi and insert the corresponding resulting output below: List of booleans: >>> :t [True, False] - +[True,False] :: [Bool] String is a list of characters: >>> :t "some string" - +"some string" :: [Char] Empty list: >>> :t [] - +[] :: [a] Append two lists: >>> :t (++) - +(++) :: [a] -> [a] -> [a] Prepend an element at the beginning of a list: >>> :t (:) - +(:) :: a -> [a] -> [a] Reverse a list: >>> :t reverse - +reverse :: [a] -> [a] Take first N elements of a list: >>> :t take - +take :: Int -> [a] -> [a] Create a list from N same elements: >>> :t replicate - +replicate :: Int -> a -> [a] Split a string by line breaks: >>> :t lines - +lines :: String -> [String] Join a list of strings with line breaks: >>> :t unlines - +unlines :: [String] -> String -} @@ -186,31 +186,33 @@ Evaluate the following expressions in GHCi and insert the answers. Try to guess first, what you will see. >>> [10, 2] ++ [3, 1, 5] +[10,2,3,1,5] >>> [] ++ [1, 4] -- [] is an empty list - +[1,4] >>> 3 : [1, 2] - +[3,1,2] >>> 4 : 2 : [5, 10] -- prepend multiple elements - +[4,2,5,10] >>> [1 .. 10] -- list ranges - +[1,2,3,4,5,6,7,8,9,10] >>> [10 .. 1] - +[] >>> [10, 9 .. 1] -- backwards list with explicit step - +[10,9,8,7,6,5,4,3,2,1] >>> length [4, 10, 5] -- list length - +3 >>> replicate 5 True - +[True,True,True,True,True] >>> take 5 "Hello, World!" - +"Hel" >>> drop 5 "Hello, World!" +", World!" >>> zip "abc" [1, 2, 3] -- convert two lists to a single list of pairs - +[('a',1),('b',2),('c',3)] >>> words "Hello Haskell World!" -- split the string into the list of words - +["Hello","Haskell","World!"] 👩‍🔬 Haskell has a lot of syntax sugar. In the case with lists, any @@ -336,8 +338,10 @@ from it! ghci> :l src/Chapter2.hs -} subList :: Int -> Int -> [a] -> [a] -subList = error "subList: Not implemented!" - +subList x y z = if ylength z then [] else + let start = drop x z + end = take (y-x+1) start + in end {- | =⚔️= Task 4 @@ -348,8 +352,11 @@ Implement a function that returns only the first half of a given list. >>> firstHalf "bca" "b" -} --- PUT THE FUNCTION TYPE IN HERE -firstHalf l = error "firstHalf: Not implemented!" +firstHalf :: [a] -> [a] +firstHalf l = + let s = length l + x = div s 2 + in take x l {- | @@ -501,7 +508,9 @@ True >>> isThird42 [42, 42, 0, 42] False -} -isThird42 = error "isThird42: Not implemented!" +isThird42 :: [Int]->Bool +isThird42 (_:_:42:_) = True +isThird42 _ =False {- | @@ -606,7 +615,8 @@ Implement a function that duplicates each element of the list -} duplicate :: [a] -> [a] -duplicate = error "duplicate: Not implemented!" +duplicate [] = [] +duplicate (x:xs)= [x] ++ [x] ++ duplicate(xs) {- | @@ -621,7 +631,9 @@ Write a function that takes elements of a list only in even positions. >>> takeEven [2, 1, 3, 5, 4] [2,3,4] -} -takeEven = error "takeEven: Not implemented!" +takeEven :: [Int] -> [Int] +takeEven [] =[] +takeEven(x:xs) = if mod x 2 == 0 then [x] ++ takeEven xs else [] ++ takeEven xs {- | =🛡= Higher-order functions @@ -728,7 +740,8 @@ value of the element itself 🕯 HINT: Use combination of 'map' and 'replicate' -} smartReplicate :: [Int] -> [Int] -smartReplicate l = error "smartReplicate: Not implemented!" +smartReplicate[]=[] +smartReplicate (x:xs) = replicate x x ++ smartReplicate xs {- | =⚔️= Task 9 @@ -741,7 +754,9 @@ the list with only those lists that contain a passed element. 🕯 HINT: Use the 'elem' function to check whether an element belongs to a list -} -contains = error "contains: Not implemented!" +contains :: Int->[[Int]] -> [[Int]] +contains _ []=[] +contains y (x:xs) = if elem y x then [x] ++ contains y xs else []++ contains y xs {- | @@ -781,13 +796,13 @@ Let's now try to eta-reduce some of the functions and ensure that we mastered the skill of eta-reducing. -} divideTenBy :: Int -> Int -divideTenBy x = div 10 x +divideTenBy = div 10 -- TODO: type ;) -listElementsLessThan x l = filter (< x) l +listElementsLessThan x = filter (< x) -- Can you eta-reduce this one??? -pairMul xs ys = zipWith (*) xs ys +pairMul = zipWith (*) {- | =🛡= Lazy evaluation @@ -842,7 +857,12 @@ list. 🕯 HINT: Use the 'cycle' function -} -rotate = error "rotate: Not implemented!" +rotate :: Int -> [a] -> [a] +rotate x s = + let y = cycle s + z = drop x y + out = take (length s) z + in out {- | =💣= Task 12* @@ -858,7 +878,9 @@ and reverses it. function, but in this task, you need to implement it manually. No cheating! -} -rewind = error "rewind: Not Implemented!" +rewind :: [a] -> [a] +rewind [] = [] +rewind(x:xs) = rewind xs ++ [x] {-