> as soon as the last thunk is read, the file is closed.
That's probably doable. It's true that when the only reference to the handle in question is the one buried in the thunk pointed at by the lazy input, it should be safe to close it when a thunk evaluates to end-of-input (or an error, for that matter).
I'm not sure whether or not it'd be applicable enough to be worth doing. The immediate issues I spot are that a lot of input streams aren't consumed all the way to the end, and that you'd have to be careful not to capture a reference anywhere else (or you'll be waiting for GC to remove that reference before the count falls to zero).
Also things like unix pipes or network sockets, where the "close" operation means something different as there are multiple parties involved. Arguably the same is true of files as you could be reading a file being simultaneously written to by others.
That's probably doable. It's true that when the only reference to the handle in question is the one buried in the thunk pointed at by the lazy input, it should be safe to close it when a thunk evaluates to end-of-input (or an error, for that matter).
I'm not sure whether or not it'd be applicable enough to be worth doing. The immediate issues I spot are that a lot of input streams aren't consumed all the way to the end, and that you'd have to be careful not to capture a reference anywhere else (or you'll be waiting for GC to remove that reference before the count falls to zero).