type FracList = [Float]

incList :: FracList -> FracList
incList = map (+1)

--sumIncList l = foldl (+) 0 (incList l)
sumIncList = foldl (+) 0 . incList
-- va rezulta sumIncList :: FracList -> Float

data FuzzyBoolean = 
              CertainTrue
            | CertainFalse
            | Uncertain

toBool CertainTrue = True
toBool CertainFalse = False
toBool Uncertain = undefined


data Natural = Zero | Succ { prev :: Natural }
        deriving (Show, Eq)

unu = Succ Zero
doi = Succ unu

addNatural Zero n = n
addNatural (Succ m) n = Succ $ addNatural m n
-- \> addNatural unu doi


infixl 6 +*
--(+*) = addNatural
Zero +* n = n
(Succ m) +* n = Succ $ m +* n
-- \> unu +* doi

{-
prev (Succ m) = m
prev Zero = undefined
-- alternativ, îl definesc pe prev odată cu tipul
-}
-- \> prev doi +* unu == doi


data MultiTuplu a   = Null
                    | Single a
                    | Pair a a
                    | Triple a a a
        deriving Show

prefix 0 l = Null
prefix 1 l = Single (head l)
prefix 2 l = Pair (head l) (l !! 1)
prefix 3 l = Triple (head l) (l !! 1) (l !! 2)
-- \> prefix 3 [1..10]

data ValueOrBool a  = IsBool {valB :: Bool}
                    | IsValue {val :: a}
              deriving Show

elemPlus e l = if elem e l 
        then IsValue e else IsBool False
-- \> val $ elemPlus 2 [1,2,3]
-- \> valB $ elemPlus 4 [1,2,3]