module AlgDataType where

data Weekday =
             Mon | Tue | Wed | Thu | Fri | Sat | Sun
                 deriving Eq 

instance Show Weekday where
    show Mon = "Monday"
    show Tue = "Tuesday"
    show Wed = "Wednesday"
    show Thu = "Thursday"
    show Fri = "Friday"
    show Sat = "Saturday"
    show Sun = "Sunday"



data IntTree = IntBranch IntTree IntTree
             | IntLeaf Int
               deriving Show

testIntTree = IntBranch (IntLeaf 1) (IntBranch (IntLeaf 3) (IntLeaf 5))

data Tree a = Branch (Tree a) (Tree a) | Leaf a

showTree :: Show a => Tree a -> String
showTree t = (showTreeIndent 0 t)
    where showTreeIndent ind t =
              let indent =  replicate ind ' ' in
                  "\n" ++
                  case t of
                    Branch l r -> indent ++ "L:" ++ 
                                  (showTreeIndent (ind + 2) l) ++ "\n" ++
                                  indent ++ "R:" ++ 
                                  (showTreeIndent (ind + 2) r) 
                    Leaf l -> indent ++ show l


instance Show a => Show (Tree a) where
  show = showTree

-- example Trees:

tr = Branch 
       (Branch 
         (Branch (Leaf 1) (Leaf 2))
         (Leaf 3))
       (Branch (Leaf 4) (Leaf 5))


-- tiny evaluator

data Term = TmInt Integer
          | TmBool  Bool
          | TmIf Term Term Term
          | TmStuck
            deriving (Show, Eq)

isValue (TmInt _) = True
isValue (TmBool _) = True
isValue _ = False

eval :: Term -> Term
eval t =
  case t of 
    tm@(TmInt _)  -> tm
    tm@(TmBool _) -> tm
    TmIf (TmBool True) th el -> eval th
    TmIf (TmBool False) th el -> eval el
    TmIf cond th el -> eval (TmIf (eval cond) th el)
--    _ -> error "Unknown Term"

-- is the evaluator type safe?


-- smallstep evaluator:

evalOne :: Term -> Term 
evalOne (TmIf (TmBool True) t2 t3) = t2
evalOne (TmIf (TmBool False) t2 t3) = t3
evalOne (TmIf t1 t2 t3) | not (isValue t1) = TmIf (evalOne t1) t2 t3
evalOne _ = TmStuck


evalStar :: Term -> Term
evalStar tm | isValue tm = tm
evalStar TmStuck = error "order pizza"
evalStar tm = evalStar . evalOne $ tm