haskell-lectures/common/code/Code.hs

module Code where

data WeekDay = Monday
             | Tuesday
             | Thursday
             | Wednsday
             | Friday
             | Saturday
             | Sunday
  deriving (Show)


f :: Int -> Int -> Int
f x 0 = 1
f x y = x * f x (y - 1)

mod2 :: Int -> Int
mod2 x
  | x - 2 == 0 = 0
  | x - 2 < 0  = x
  | otherwise  = mod2 (x - 2)

week :: [WeekDay]
week = [Monday, Tuesday, Thursday, Wednsday
       , Friday, Saturday, Sunday]

isMonday :: WeekDay -> Bool
isMonday Monday = True
isMonday x      = False

data Tree = Leaf Char
          | Node Tree Int Tree
  deriving Show

data MaybeInt = NoError Int
              | Error String

calcSomething :: Int -> MaybeInt
calcSomething x
  | x < 100   = NoError (x * 5)
  | otherwise = Error "Int out of range!"


f' :: Int -> Int
f' x = let y p = x + p
       in x + (y 2)

addTwo :: [Int] -> [Int]
addTwo [] = []
addTwo (x:xs) = (x + 2) : addTwo xs

f'' :: String -> Bool
f'' xs = even . length . (\x -> x ++ "Hello world") $ xs

g :: Int -> Bool
g x = case x - 2 of
  2 -> True
  5 -> True
  x -> False