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|
-- This are my solutions to the exercises from https://github.com/moocfi/haskell-mooc
import Data.List
---------
-- Set.01
-- https://github.com/moocfi/haskell-mooc/blob/master/exercises/Set1.hs
-- Ex. 1
one :: Integer -- function declaration: types of arguments and output
one = 1 -- function definition
two :: Integer
two = 2
-- Ex. 2
double :: Integer -> Integer
double x = x * 2
-- Ex. 3
quadruple :: Integer -> Integer
quadruple x = double (double x)
-- Ex. 4
distance :: Double -> Double -> Double -> Double -> Double
-- exponentiation operator: ^ for integers, ^^ for fractionals and ** for floating point
distance x1 y1 x2 y2 = sqrt (abs(x1 - x2)**2 + abs(y1 - y2)**2)
-- Ex. 5
eeny :: Integer -> String
eeny x = if even x
then "eeny"
else "meeny"
-- Ex. 6
checkPassword :: String -> String
checkPassword password = if password == "swordfish" || password == "mellon"
then "You're in."
else "ACCESS DENIED!"
-- Ex. 7
postagePrice :: Int -> Int
postagePrice weight = if weight > 5000 then 6000
else if weight > 500 then 300 + weight * 1
else 250
-- Ex. 8
isZero :: Int -> Bool
isZero 0 = True -- this is pattern matching
isZero x = False
-- Ex. 9
sumTo :: Int -> Int
sumTo 1 = 1
sumTo n = n + sumTo (n - 1)
-- Ex. 10
power :: Int -> Int -> Int
power n 1 = n
power n k = n * power n (k - 1)
-- Ex. 11
ilog3 :: Int -> Int
ilog3 0 = 0
ilog3 n = 1 + ilog3 (div n 3)
----------
-- Set.02a
-- https://github.com/moocfi/haskell-mooc/blob/master/exercises/Set2a.hs
-- Functions you'll need: head, tail, take, drop, length, null
-- Ex. 1
years = [1982, 2004, 2020]
-- Ex. 2
takeFinal :: Int -> [a] -> [a] -- a is the Haskell equivalent of generics (T) in C#
takeFinal n xs
| n > length xs = xs
| otherwise = drop (length xs - n) xs
-- Ex. 3
updateAt :: Int -> a -> [a] -> [a]
-- elements before i + x + elemenets after i ; ++ concatenates arrays
updateAt i x xs = take i xs ++ [x] ++ drop (i + 1) xs
-- Ex. 4
substring :: Int -> Int -> String -> String
substring i j s = drop i (take j s)
-- Ex. 5
isPalindrome :: String -> Bool
isPalindrome s = s == reverse s
-- Ex. 6
palindromify :: String -> String
palindromify s = if isPalindrome s then s -- can easily make it: if s == reverse s then s , but decided this way was more readable
else palindromify (take (length s - 2) (drop 1 s))
-- Ex. 7
safeDiv :: Int -> Int -> String
safeDiv x y
| y == 0 = "Nothing"
| otherwise = "Just " ++ show (div x y) -- show casts the value to string
-- Ex. 8
greet :: String -> Maybe String -> String -- maybe means the value can (String) or can not be given (Nothing) ; you need to use pattern matching
greet firstName Nothing = "Hello, " ++ firstName ++ "!"
greet firstName (Just lastName) = "Hello, " ++ firstName ++ " " ++ lastName ++ "!"
-- Ex. 9
safeIndex :: [a] -> Int -> Maybe a
safeIndex xs i = if 0 > i || i >= length xs then Nothing
else Just (xs !! i)
-- Ex. 10
eitherDiv :: Int -> Int -> Either String Int -- a value can be the left one or the right one (specified when given)
eitherDiv x 0 = Left (show x ++ "/0")
eitherDiv x y = Right (div x y)
-- Ex. 11
addEithers :: Either String Int -> Either String Int -> Either String Int
addEithers (Right x) (Right y) = Right (x + y)
addEithers (Right x) (Left y) = Left y
addEithers (Left x) (Right y) = Left x
|
