Each instance of a stream has an ~abstract~ data pointer that can hold underlying resource handle(s) and other stateful data required by your stream. Lets see how to write a very simple file based stream, using POSIX IO. struct my_stream_data { int filedes; } When we create our stream, we will store a pointer to the above structure in the ~abstract~ field of the stream structure. We can now move on and write the core operations for our stream...