module Work where

-- A datatype for lists
-- data ListOfInt   = Empty  | Add  Integer ListOfInt
-- data ListOfFloat = Empty' | Add' Float   ListOfFloat

data List a = Empty | Add a (List a)

-- 1,2,3
list1 :: List Integer
list1 = Add 1 (Add 2 (Add 3 Empty))

-- 2.3, 3.4
list2 :: List Float
list2 = Add 2.3 (Add 3.4 Empty)

data FI = F Float | I Integer

-- A list with elements of different type
list3 :: List FI
list3 = Add (F 2.3) (Add (I 4) Empty)

pair1 :: (Float, Integer)
pair1 = (2.3, 4)

-- Slides: type of constructors

-- Socrative: type of isNumeric

-- Use List to define Hand
-- type Hand = List Card

-- tom l checks whether l is empty
tom :: List t -> Bool
tom Empty = True
tom _     = False
  -- Type variables begins with a small letter

-- forst list returns the first element of the list
forst :: List t -> t
forst Empty     = error "forst: empty list"
forst (Add a _) = a

-- sist l returns the last element of l
sist :: List t -> t
sist Empty         = error "sist: empty list"
sist (Add a Empty) = a
sist (Add a as)    = sist as

-- Slides: standard lists

-- Define these functions for the standard lists

-- size l (a.k.a length) returns the number of elements in l
size' :: List a -> Integer
size' Empty      = 0
size' (Add a as) = 1 + size' as

size :: [a] -> Integer
size []     = 0
size (_:as) = 1 + size as

-- summan xs (a.k.a sum) calculates the sum of all elements in xs
summan :: Num a => [a] -> a
summan []     = 0
summan (x:xs) = x + summan xs
  -- What is the most general type of summan?

-- Socrative: definition of mest

-- mest l (a.k.a. maximum) returns the largest element in l

-- l1 +++ l2 (a.k.a. ++) appends l2 after l1

-- rev (a.k.a. reverse) reverses the elements in l

-- value s returns the number represented by the string s as an integer
  -- Property of value and show