edicl
Setting flexi-stream-position has no effect on the next byte read
Running
(with-open-file (in "2-byte-file" :element-type '(unsigned-byte 8))
(setq in (make-flexi-stream in))
(setf (flexi-stream-position in) 1)
(read-byte in))
returns the first byte, while I would expect the second byte. This happens on SBCL for me. I don't know if it's a bug or intended behavior, however in the latter case might be good to update the documentation.
The behavior of (setf flexi-stream-position) isn't documented anywhere. You should use FILE-POSITION.
Hi. Thanks for a quick response. file-position does not report correct flexi-stream position after peek-byte, nor does it set the correct position. This is per documentation, I think, "FILE-POSITION for flexi streams will work as if the function had been applied to the underlying stream." Suppose I'm reading in a file, use peek-byte at times, and then I want to shift the position in the flexi-stream. Neither flexi-stream-position nor file-position can currently do it, I think.
Is the issue with double buffering? I.e. file-position should clear the flexi-stream buffer of unread bytes?
Suppose I am reading a stream, using peek-byte sometimes, and now I want to jump back a number of bytes. If file-position would clear the buffer of unread bytes, I can do that, but the code will look counterintuitive. First, read the current position with flexi-stream-position. Second, set the new position with file-position. Would it not be more intuitive to use (setf (flexi-stream-position) ...) for that?
I'm not at all familiar with flexi-stream, just started playing with it this week. What I was looking for is to have peek-byte functionality and the ability to move back and forth within the stream, like it exists with file-position in standard streams. Well, (setf (flexi-stream-position) ...) is at least listed in the documentation, so I gave it a spin, but it does something different. I don't have a strong opinion on how best to implement the functionality I discuss.
flexi-stream-position is not really properly documented, so the most intuitive thing would be not to have it and only rely on file-position. Which, at the moment, doesn't play well with the buffering that flexi-streams is performing.