Haskell Chapter 5

module Main where

import Data.Char (isUpper)

-- HC5T1: Using applyThrice
applyThrice :: (a -> a) -> a -> a
applyThrice f x = f (f (f x))

-- HC5T2: Filtering Odd Numbers
filterOddNumbers :: [Int] -> [Int]
filterOddNumbers = filter odd

-- HC5T3: Checking for Uppercase Letters
hasUppercaseStart :: [String] -> Bool
hasUppercaseStart = any (\word -> not (null word) && isUpper (head word))

-- HC5T4: Using Lambda Functions
biggerThan10Lambda :: Int -> Bool
biggerThan10Lambda = \x -> x > 10

-- HC5T5: Partial Application
multiplyByFive :: Int -> Int
multiplyByFive = (* 5)

-- HC5T6: Function Composition
squareAndFilterEven :: [Int] -> [Int]
squareAndFilterEven = filter even . map (^2)

-- HC5T7: The $ Operator
result :: Int
result = sum $ map (*2) $ filter (>3) [1..10]

-- HC5T8: Point-Free Style
addFive :: Int -> Int
addFive = (+ 5)

-- HC5T9: Higher-Order Function to Transform a List
transformList :: (a -> a) -> [a] -> [a]
transformList f = map (f . f)

-- HC5T10: Combining Higher-Order Functions
anySquaredGreaterThan50 :: [Int] -> Bool
anySquaredGreaterThan50 = any (>50) . map (^2)


-- Main function to test all tasks
main :: IO ()
main = do
  putStrLn "--- HC5T1: applyThrice Tests ---"
  print (applyThrice (+1) 0)
  print (applyThrice (*2) 1)
  print (applyThrice (`div` 2) 16)

  putStrLn "\n--- HC5T2: Filtering Odd Numbers Tests ---"
  print (filterOddNumbers [1..30])

  putStrLn "\n--- HC5T3: Checking for Uppercase Letters Tests ---"
  print (hasUppercaseStart ["hello", "World", "Haskell"])
  print (hasUppercaseStart ["apple", "banana", "cat"])
  print (hasUppercaseStart [])
  print (hasUppercaseStart ["", "Test"])

  putStrLn "\n--- HC5T4: Using Lambda Functions Tests ---"
  print (biggerThan10Lambda 15)
  print (biggerThan10Lambda 8)

  putStrLn "\n--- HC5T5: Partial Application Tests ---"
  print (multiplyByFive 10)
  print (multiplyByFive 3)

  putStrLn "\n--- HC5T6: Function Composition Tests ---"
  print (squareAndFilterEven [1, 2, 3, 4, 5, 6])

  putStrLn "\n--- HC5T7: The $ Operator Tests ---"
  print result

  putStrLn "\n--- HC5T8: Point-Free Style Tests ---"
  print (addFive 10)
  print (addFive 0)

  putStrLn "\n--- HC5T9: Higher-Order Function to Transform a List Tests ---"
  print (transformList (+1) [1, 2, 3])
  print (transformList (*2) [1, 2, 3])

  putStrLn "\n--- HC5T10: Combining Higher-Order Functions Tests ---"
  print (anySquaredGreaterThan50 [1, 5, 6, 7])
  print (anySquaredGreaterThan50 [1, 5, 6, 8])
  print (anySquaredGreaterThan50 [])