problem with zero-length sequences

[gamorris]

I'm getting:

> (cl-pack:unpack "a0" "" :consumed 0)
0
NIL
> (cl-pack:unpack "a0" "zyxw" :consumed 0)
"z"
1

I think ideally it should be:

> (cl-pack:unpack "a0" "" :consumed 0)
NIL
0
> (cl-pack:unpack "a0" "zyxw" :consumed 0)
NIL    ; or maybe "" ?
0

I came across this when I was trying to decode a length-prefixed list of structures. I was trying to use a pattern like "l/(CCCl/a)". For some of my input data the list has length zero, so the input string is effectively equivalent to (cl-pack:pack "l" 0). I.e., ultimately I would like for this to work: (cl-pack:unpack "l/a" (cl-pack:pack "l" 0)) (e.g. return nil). At the moment I get a type error: The value NIL is not of the expected type NUMBER. (Running on Clozure CL on a Mac.)

Looking through the code it looked like the "a0" issue is likely the cause of "l/a" with a zero length giving an error.

This is not critical for me...I already coded a work-around. Simply a nice-to-have. (If I have some spare time I will see if I can come up with a patch myself. In the mean time it seemed worth reporting.)

Thanks!