Haskell for Taquerias

taqueria.hs

foo :: Int
foo = 5

incr :: Int -> Int
incr x = x + 1

decr :: Int -> Int
decr x = x - 1

nada :: Int -> Int
nada = incr . decr

nada' :: Int -> Int
nada' x = incr $ decr 1

add :: Int -> Int -> Int
add x y = x + y

fac :: Int -> Int
fac 1 = 1
fac n | n > 1 = n * fac (n-1)
fac _ = error "bad"

fib :: Int -> Int
fib 1 = 1
fib 2 = 1
fib n = fib (n-1) + fib (n-2)

fibs = 1 : 1 : zipWith (+) fibs (tail fibs)

map' ::  (a -> b) -> [a] -> [b]
map' f [] = []
map' f (x:xs) = (f x):(map' f xs)

filter' :: (a -> Bool) -> [a] -> [a]
filter' f [] = []
filter' f (x:xs) | f x = x : filter' f xs
                 | otherwise = filter' f xs

-- Data

data Salsa = Tomatillo | Chipotle | Mango | Custom String | Mix [Salsa]

explode :: [String] -> String -> String
explode  [] _ = []
explode [x] _ = x
explode (x:xs) separator = x ++ separator ++ explode xs separator

salsaDescription :: Salsa -> String
salsaDescription Tomatillo = "green"
salsaDescription Chipotle = "smokey"
salsaDescription Mango = "sweet"
salsaDescription (Custom desc) = desc ++ " salsa"
salsaDescription (Mix salsas) = "Mix of " ++ explode (map salsaDescription salsas) ", "

data List a = ListEmpty | Node a (List a)

list1 = ListEmpty
list2 = (Node 5 ListEmpty)
list3 = (Node 5 ( Node 6 ListEmpty))

data Tree a = TreeEmpty | TreeNode a (Tree a) (Tree a)

tree1 = TreeEmpty
tree2 = TreeNode 6
                 TreeEmpty
                 (TreeNode 6 TreeEmpty TreeEmpty)

sumTree :: (Tree Int) -> Int
sumTree TreeEmpty = 0
sumTree (TreeNode v left right) = v + (sumTree left) + (sumTree right)


salsaPreferences = [("Raphie", Chipotle), ("Lyall", Mango)]

salsaGreeting :: String -> String
salsaGreeting name = "Hey " ++ name ++ ", your favorite salsa is " ++ safeDescription salsa
  where salsa = lookup name salsaPreferences
        safeDescription Nothing = "an unknown salsa"
        safeDescription (Just salsa) = salsaDescription salsa

wallize :: Int -> String
wallize n = (show n) ++ " beers on the wall"

beersOnTheWall :: Int -> [String]
-- beersOnTheWall 0 = []
-- beersOnTheWall n = (beersOnTheWall (n-1)) ++ [wallize n]
-- Lazy Approach:
beersOnTheWall n = take n (map wallize [1..])

-- main = interact (unlines . reverse . lines)
main = interact reverse