:: Main a = {main :: a}
:: UserLED = LED1 | LED2 | LED3

class seq v where
  (:.) infixr 0 :: (v t p) (v u q) -> v u Stmt | ...
class assign v where
  (=.) infixr 2 :: (v t Upd) (v t p) -> v t Expr | type t & isExpr p
class noOp v where noOp :: v t p
class IF v where
  IF :: (v Bool p) (v t q) (v s r) -> v () Stmt | isExpr p
  (?) infix 1 :: (v Bool p) (v t q) -> v () Stmt | isExpr p
class userLed v where
  ledOn :: UserLED -> (v () Stmt)
  ledOff :: UserLED -> (v () Stmt)