YesNo1.hs

module YesNo1 where

-- weakly typed JS string.length > 0 = True functionality   

class YesNo a where  
    yesno :: a -> Bool

instance YesNo Int where  
    yesno 0 = False  
    yesno _ = True 

instance YesNo [a] where  
    yesno [] = False  
    yesno _ = True  

--id? It's just a standard library function that takes a parameter and returns the same thing
instance YesNo Bool where  
    yesno = id 

instance YesNo (Maybe a) where  
    yesno (Just _) = True  
    yesno Nothing = False  

instance YesNo (Tree a) where  
    yesno EmptyTree = False  
    yesno _ = True  

instance YesNo TrafficLight where  
    yesno Red = False  
    yesno _ = True  

-- ghci> yesno $ length []  
-- False  
-- ghci> yesno "haha"  
-- True  
-- ghci> yesno ""  
-- False  
-- ghci> yesno $ Just 0  
-- True  
-- ghci> yesno True  
-- True  
-- ghci> yesno EmptyTree  
-- False  
-- ghci> yesno []  
-- False  
-- ghci> yesno [0,0,0]  
-- True  
-- ghci> :t yesno  
-- yesno :: (YesNo a) => a -> Bool 

yesnoIf :: (YesNo y) => y -> a -> a -> a  
yesnoIf yesnoVal yesResult noResult = if yesno yesnoVal then yesResult else noResult  

-- ghci> yesnoIf [] "YEAH!" "NO!"  
-- "NO!"  
-- ghci> yesnoIf [2,3,4] "YEAH!" "NO!"  
-- "YEAH!"  
-- ghci> yesnoIf True "YEAH!" "NO!"  
-- "YEAH!"  
-- ghci> yesnoIf (Just 500) "YEAH!" "NO!"  
-- "YEAH!"  
-- ghci> yesnoIf Nothing "YEAH!" "NO!"  
-- "NO!"