TL;DR: linear-base seems to not provide me with a way to turn functions of type Handle -> IO a into Handle %1 -> RIO (Ur? a, Handle), and this seems to stop me from doing anything with ByteString.

I am trying to build a library to parse (and later, write) a data archive format from an old game, and do it with linear types to stretch myself. The file begins with a header listing the contents of all files in the archive, and their byte offsets into the archive itself. I want to write a function to return a ByteString stream from a Handle, when given the Record describing the name/offset/etc.

If I was using standard Haskell, I would write something like this, and trust the user not to abuse the Handle while streaming (we must hSeek to the offset and then stream the required number of bytes:

hGetRecord :: MonadIO m => Record -> Handle -> ByteStream m ()

But in linear-base, we seem to hit the following:

1. We can't use the standard streaming types, we have to use the one in Streaming.Linear.
2. This means we can't use the streaming-bytestring ByteStream type, and must use Stream (Of ByteString) from linear-base. Annoying, but OK.

The function I think I want to write with linear types:

hGetRecord :: Record -> Handle %1 -> Stream (Of ByteString) RIO Handle

This should let me safely seek the handle, without anyone interfering with it until the streaming is finished. But I cannot lift the ByteString I/O functions from System.IO.IO to RIO because the constructor for System.IO.Linear.Resource.Handle is not exported.

Describe the solution you'd like

I think that variants of unsafeFromSystemIOResource etc that allow me to bring Handle-using IO functions into RIO and have them play nicely with the existing Handle type in linear-base would give me everything I need, but that's probably an unsafe level of power. The functions I need are RIO versions of:

• openBinaryFile
• hSeek
• Data.ByteString.Lazy.hGet