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module Calc where
import ExprT
import Parser
-- Exercise 1
eval :: ExprT -> Integer
eval (Lit n) = n
eval (Add l r) = eval l + eval r
eval (Mul l r) = eval l * eval r
-- Exercise 2
evalStr :: String -> Maybe Integer
evalStr s = case parseExp Lit Add Mul s of
Nothing -> Nothing
Just t -> Just (eval t)
-- Exercise 3
class Expr a where
lit :: Integer -> a
add :: a -> a -> a
mul :: a -> a -> a
instance Expr ExprT where
lit = Lit
add = Add
mul = Mul
reify :: ExprT -> ExprT
reify = id
-- Exercise 4
instance Expr Integer where
lit x = x
add l r = eval (Add (Lit l) (Lit r))
mul l r = eval (Mul (Lit l) (Lit r))
instance Expr Bool where
lit x
| x <= 0 = False
| otherwise = True
add = (||)
mul = (&&)
newtype MinMax = MinMax Integer deriving (Eq, Show)
newtype Mod7 = Mod7 Integer deriving (Eq, Show)
instance Expr MinMax where
lit = MinMax
add (MinMax l) (MinMax r) = MinMax (max l r)
mul (MinMax l) (MinMax r) = MinMax (min l r)
instance Expr Mod7 where
lit x = Mod7 (mod x 7)
add (Mod7 l) (Mod7 r) = Mod7 (mod (l + r) 7)
mul (Mod7 l) (Mod7 r) = Mod7 (mod (l * r) 7)
testExp :: Expr a => Maybe a
testExp = parseExp lit add mul "(3 * -4) + 5"
testInteger = testExp :: Maybe Integer
testBool = testExp :: Maybe Bool
testMM = testExp :: Maybe MinMax
testSat = testExp :: Maybe Mod7
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