module skeleton12

import StdEnv
import StdMaybe

:: BM a b = {t :: a -> b, f :: b -> a}                                          
bm :: BM a a
bm = {f=id, t=id}
:: Expr a
	= Lit (BM a Int) Int
	| Add (BM a Int) (Expr a) (Expr a)
	| Mul (BM a Int) (Expr a) (Expr a)
	| Read
	| Write (BM a a) (Expr a)
	| XOR (BM a a) (Expr a) (Expr a)
	| Not (BM a a) (Expr a)
	| E.b: Eq (BM b a) (Expr b) (Expr b) & == b
	| Throw
	| Try (BM a a) (BM a a)

class show a where
	show :: (a t) [String] -> [String] | toString t

instance show Expr where
	show (Lit bm x) xs = [toString x:xs]
	show (Add bm x y) xs = show x ["+":show y xs]
	show (Mul bm x y) xs = show x ["*":show y xs]
	show Read xs = ["read":xs]
	show (Write bm x) xs = ["write":show x xs]
	show (XOR bm x y) xs = show x ["XOR":show y xs]
	show (Not bm x) xs = show x xs
	show (Eq bm x y) xs = show x ["==":show y xs]
	show Throw xs = ["throw":xs]
	show (Try x y) xs = ["try":show x ["catch":show y xs]]

Start = 1