module test

import StdEnv

class expr v c
where
	lit :: a -> v (c a)

//class plus v c
//where
//	(+.) infixl 6 :: (v c a) (v c a) -> v c a | + a

:: BM x y = { to :: x -> y, fro :: y -> x }
bm :: BM a a
bm = {to=id, fro=id}

:: ToString a = E.e: ToString (BM a e) & toString e

:: Printer a = P a ([String] -> [String])
:: PrintConstraints a = E.e: PC (BM a e) & toString e

print :: (Printer (PrintConstraints a)) -> [String]
print (P _ a) = a []

instance expr Printer PrintConstraints
where
	lit a = P (PC bm) \c->[toString (bm.to a):c]
//instance plus Printer PrintConstraints
//where
//	(+.) (P l) (P r) = P \c->["(":l ["+":r [")":c]]]

//:: Eval c a = E a | EBlurp (c a)
//:: EvalConstraints a = EC a
//eval :: (Eval EvalConstraints a) -> a
//eval (E a) = a
//
//instance expr Eval EvalConstraints
//where
//	lit a = E a
//instance plus Eval PrintConstraints
//where
//	(+.) (E l) (E r) = E (l + r)

Start = print t
where
	t = lit 42