diff --git a/src/Chapter1.hs b/src/Chapter1.hs index 406deeac..3d359eb2 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 a => a 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 - +100 >>> 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) @@ -449,7 +449,7 @@ Implement the function that takes an integer value and returns the next 'Int'. function body with the proper implementation. -} next :: Int -> Int -next x = error "next: not implemented!" +next x = x + 1 {- | After you've implemented the function (or even during the implementation), you @@ -490,7 +490,10 @@ Implement a function that returns the last digit of a given number. whether it works for you! -} -- DON'T FORGET TO SPECIFY THE TYPE IN HERE -lastDigit n = error "lastDigit: Not implemented!" + +-- lastDigit :: Integral a => a -> a +lastDigit :: Int -> Int +lastDigit n = mod n 10 {- | @@ -520,7 +523,13 @@ 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 x == y + then x + else + if abs x <= abs y + then x + else y {- | @@ -553,8 +562,8 @@ 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 + z - max (max x y) z - min (min x y) z {- | =⚔️= Task 8 @@ -568,7 +577,10 @@ True >>> isVowel 'x' False -} -isVowel c = error "isVowel: not implemented!" +isVowel :: Char -> Bool +isVowel c + | c == 'a' || c == 'e' || c == 'i' || c == 'o' || c == 'u' || c == 'y' = True + | otherwise = False {- | @@ -632,7 +644,18 @@ 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 helpNum = mod n 100 + in div helpNum 10 + lastDigit helpNum + +sumLast2where :: Int -> Int +sumLast2where n = div (last2 n) 10 + lastDigit (last2 n) + where + last2 :: Int -> Int + last2 helpNum = mod helpNum 100 + {- | @@ -653,7 +676,10 @@ 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 + | abs n < 10 = abs n + | otherwise = firstDigit (div (abs n) 10) {- @@ -668,3 +694,4 @@ Modules: http://learnyouahaskell.com/modules Let vs where: https://wiki.haskell.org/Let_vs._Where Packages and modules in Haskell: https://downloads.haskell.org/~ghc/latest/docs/html/users_guide/packages.html -} + diff --git a/src/Chapter2.hs b/src/Chapter2.hs index b98ceaf7..a883c328 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" :: String 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 +186,31 @@ 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 >>> [10 .. 1] - +[1,2,3,4,5,6,7,8,9,10] >>> [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!" - +"Hello" >>> 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 @@ -335,8 +335,15 @@ from it! ghci> :l src/Chapter2.hs -} +import Data.List +import GHC.CmmToAsm.AArch64.Instr (_d) +import GHC.Base (VecElem(Int16ElemRep), Alternative (empty)) + subList :: Int -> Int -> [a] -> [a] -subList = error "subList: Not implemented!" +subList x y zs + | (x>=0) && (y>=0) && (y>=x) = drop x (take (y+1) zs) + | otherwise = [] + {- | =⚔️= Task 4 @@ -349,7 +356,11 @@ Implement a function that returns only the first half of a given list. "b" -} -- PUT THE FUNCTION TYPE IN HERE -firstHalf l = error "firstHalf: Not implemented!" +firstHalf :: [a] -> [a] +firstHalf l = take len l + where + len :: Int + len = div (length l) 2 {- | @@ -501,9 +512,12 @@ True >>> isThird42 [42, 42, 0, 42] False -} -isThird42 = error "isThird42: Not implemented!" +isThird42 :: [Int] -> Bool +isThird42 (_:(_:(42:_))) = True +isThird42 _ = False + {- | =🛡= Recursion @@ -535,6 +549,7 @@ For example, we can patch the previous function to count the number of steps we need to take in order to reduce the number to zero. 🤔 Blitz question: can you guess what this number represents? +-- 'go' is the recursion moved into a seperate function, it takes two numbers (end condition, input number n) of Int and returns the counts as Int (output number n) devided by 2 recursively. Maybe it could be a performance indicator like O-notation of its own function O(n). @ divToZero :: Int -> Int @@ -606,7 +621,8 @@ 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 +637,29 @@ 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 ) = x : takeEven xs +takeEven x = x + +takeOdd :: [Int] -> [Int] +takeOdd [] = [] +takeOdd (_ : x : xs ) = x : takeOdd xs +takeOdd _ = [] + +-- return only even input +takeEven2 :: [Int] -> [Int] +takeEven2 [] = [] +takeEven2 (x:xs) + | even x = x : takeEven2 xs + | odd x = takeEven2 xs + +-- return only only input +takeOdd2 :: [Int] -> [Int] +takeOdd2 [] = [] +takeOdd2 (x:xs) + | odd x = x : takeOdd2 xs + | even x = takeOdd2 xs {- | =🛡= Higher-order functions @@ -728,7 +766,12 @@ value of the element itself 🕯 HINT: Use combination of 'map' and 'replicate' -} smartReplicate :: [Int] -> [Int] -smartReplicate l = error "smartReplicate: Not implemented!" +smartReplicate = concatMap (\x -> replicate x x) +-- smartReplicate xs = concatMap (\x -> replicate x x) xs +-- smartReplicate xs = concat (map (\x -> replicate x x) xs) +-- smartReplicate [] = [] +-- smartReplicate (x:xs) = replicate x x : smartReplicate xs + {- | =⚔️= Task 9 @@ -741,8 +784,11 @@ 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 x = filter (elem x) +-- contains x = filter (\xs -> (elem x xs)) +-- contains x = filter (\xs -> x `elem` xs) +-- contains x lol = filter (\xs -> x `elem` xs) lol {- | =🛡= Eta-reduction @@ -781,13 +827,19 @@ 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 +-- divideTenBy x = div 10 x + -- TODO: type ;) -listElementsLessThan x l = filter (< x) l +listElementsLessThan :: Int -> [Int] -> [Int] +listElementsLessThan x = filter ( [a] -> [a] -> [a] +pairMul = zipWith (*) +-- pairMul xs ys = zipWith (*) xs ys {- | =🛡= Lazy evaluation @@ -842,7 +894,10 @@ list. 🕯 HINT: Use the 'cycle' function -} -rotate = error "rotate: Not implemented!" +rotate :: Int -> [a] -> [a] +rotate x ys + | x >= 0 = drop x (take (x + length ys) $ cycle ys) + | otherwise = [] {- | =💣= Task 12* @@ -858,10 +913,16 @@ 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 l = head rotateOneLess : rewind (tail rotateOneLess) + where + rotateOneLess = rotate (length l - 1) l +-- rewind l = head (rotate (length l - 1) l) : rewind (tail (rotate (length l - 1) l)) +-- rewind l = head (drop (length l - 1) l) : rewind (take (length l - 1) l) {- You did it! Now it is time to open pull request with your changes and summon @vrom911 for the review! -} +