-- | Apply an arithmetic operator to two values.
arith :: Val Int -> ArithOp ty -> Val Int -> Exp '[] ty
arith (IntVal n1) Plus     (IntVal n2) = IntE (n1 + n2)
arith :: Val Int -> ArithOp ty -> Val Int -> Exp '[] ty
arith (IntVal n1) Plus     (IntVal n2) = IntE (n1 + n2)
arith (IntVal n1) Plus     (IntVal n2) = IntE (n1 + n2)