diff --git a/src/Chapter1.hs b/src/Chapter1.hs index 04fed0db..be16d318 100644 --- a/src/Chapter1.hs +++ b/src/Chapter1.hs @@ -72,6 +72,7 @@ the `.hs` extension. -} module Chapter1 where +import Data.List {- | In Haskell, we have __expressions__. Expressions can be represented by some primitive values (numbers: 1, 100; characters: 'a', 'z'; booleans: True, False; @@ -209,31 +210,31 @@ 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 +302,43 @@ 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 @@ -429,6 +430,7 @@ task is to specify the type of this function. 49 -} +squareSum :: Int -> Int -> Int squareSum x y = (x + y) * (x + y) @@ -448,8 +450,9 @@ 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 x = x + 1 {- | After you've implemented the function (or even during the implementation), you @@ -490,7 +493,8 @@ 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 :: Int -> Int +lastDigit n = mod n 10 {- | @@ -520,7 +524,7 @@ 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 = min (abs x) (abs y) {- | @@ -553,8 +557,8 @@ 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 = head (tail(sort[x,y,z])) {- | =⚔️= Task 8 @@ -568,7 +572,10 @@ True >>> isVowel 'x' False -} -isVowel c = error "isVowel: not implemented!" +isVowel :: Char -> Bool +isVowel c + | elem c ['a', 'e', 'i', 'o', 'u'] = True + | otherwise = False {- | @@ -631,8 +638,11 @@ 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 digit1 = mod n 10 + digit2 = mod (div n 10) 10 + in digit1 + digit2 {- | @@ -653,7 +663,10 @@ 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 = n + | otherwise = firstDigit (div n 10) {- diff --git a/src/Chapter2.hs b/src/Chapter2.hs index f7c02ce2..5b863280 100644 --- a/src/Chapter2.hs +++ b/src/Chapter2.hs @@ -39,6 +39,7 @@ Now, if you are ready, bring it on! -} module Chapter2 where +-- import GHC.IO.Device (IODevice(dup)) {- =🛡= Imports @@ -136,43 +137,43 @@ 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 -} @@ -186,30 +187,43 @@ 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!" +"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!"] @@ -336,7 +350,9 @@ from it! ghci> :l src/Chapter2.hs -} subList :: Int -> Int -> [a] -> [a] -subList = error "subList: Not implemented!" +subList start stop list + | start < 0 || stop < 0 || stop < start = [] + | otherwise = drop start (take (stop+1) list) {- | =⚔️= Task 4 @@ -349,9 +365,10 @@ 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 = + let wantedLen = div (length l) 2 + in take wantedLen l {- | =🛡= Pattern matching @@ -501,7 +518,9 @@ True >>> isThird42 [42, 42, 0, 42] False -} -isThird42 = error "isThird42: Not implemented!" +isThird42 :: [Int] -> Bool +isThird42 (_:_:42:_) = True +isThird42 _ = False {- | @@ -606,7 +625,8 @@ 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 +641,10 @@ 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:xs) = x : takeEven xs {- | =🛡= Higher-order functions @@ -728,7 +751,7 @@ value of the element itself 🕯 HINT: Use combination of 'map' and 'replicate' -} smartReplicate :: [Int] -> [Int] -smartReplicate l = error "smartReplicate: Not implemented!" +smartReplicate l = concat (map (\x -> replicate x x) l) {- | =⚔️= Task 9 @@ -741,7 +764,9 @@ 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 :: (Foldable t, Eq a) => a -> [t a] -> [t a] +contains n lists = filter (elem n ) lists {- | @@ -781,13 +806,15 @@ 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 :: Int -> [Int] -> [Int] +listElementsLessThan x = filter (< x) -- Can you eta-reduce this one??? -pairMul xs ys = zipWith (*) xs ys +pairMul :: [Int] -> [Int] -> [Int] +pairMul = zipWith (*) {- | =🛡= Lazy evaluation @@ -842,7 +869,10 @@ list. 🕯 HINT: Use the 'cycle' function -} -rotate = error "rotate: Not implemented!" +rotate :: Int -> [Int] -> [Int] +rotate n list + | n < 0 = [] + | otherwise = take (length list) (drop n (cycle list)) {- | =💣= Task 12* @@ -858,7 +888,13 @@ 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 l = go l [] + where + go :: [a] -> [a] -> [a] + go [] acc = acc + go (x:xs) acc = go xs (x:acc) + {-