linear type File
	{ handle : i32 }

	--a private type, "evidence" for file state
	adt Opened<File f>{ c_opened :: Opened<f> }
	adt Closed<File f>{ c_closed :: Closed<f> }

	static new :: () -> (f::File, Closed f)

	open :: Path -> Either (f::File, Closed f, Error) (f::File, Opened f)

	read :: Opened this -> int -> Either (f::File , Closed f, Error) (f::File, Opened f, Bytes)
	write :: Opened this -> Bytes -> Either (f::File, Closed f, Error) (f::File, Opened f)

	close :: Opened this -> (f::File, Closed f)


File.new () =
	let
		f = file { InvalidHandle }
	in
		(f, c_closed f)

File.open this path =
	let h = fopen(path, "rw")
	in if h == 0
	then let f = File{h} in (Left f, c_closed f, "can't open the file")
	else (Right f, c_opened f)