module Week10 where

data List = Empty | Cons Int List
   deriving (Eq, Show)

myShow :: List -> String
myShow Empty = "*"
myShow (first `Cons` rest) = (show first)++"-"++(myShow rest)


myHead :: List -> Int
myHead Empty = error "myHead: can't find head of empty list"
myHead (Cons first _) = first 

myTail :: List -> List
myTail Empty         = error "myTail: can't find tail of empty list"
myTail (Cons _ rest) = rest


-- unit tests
numTests :: Int 
numTests = 4

passAll :: Bool
passAll = pass [1 .. numTests]

pass :: [Int] -> Bool
pass [] = True
pass (firstTest:restTests) = (test firstTest) && (pass restTests)

test :: Int -> Bool 
test 1 = (Cons 4 (Cons 2 emptyList)) == list42

test 2 
   | (myShow list42)    /= "4-2-*" = False
   | (myShow emptyList) /= "*"     = False
   | otherwise                     = True

test 3 = (myHead list42) == 4

test 4 = (myTail list42) == list2

-- some sample lists

emptyList :: List 
emptyList = Empty

list42 :: List
list42 = Cons 4 (Cons 2 (Empty))

list2 :: List
list2 = Cons 2 (Empty)





















data Tree = Leaf | Node Tree Tree
  deriving (Show, Eq)