Should we use :unspecific based on a whitelist of known-working implementations, or should we just avoid it altogether?
Either of those seems OK to me. I think a blacklist is probably wrong, just because it's too hard to update.
Agreed.
OTOH, I don't really understand the motivation in two places here:
- I don't understand the rationale for the prohibition in the CLHS
(probably someone from one of the implementation groups can say something about this) and
For backwards-compatibility probably, the CLHS allowed implementations to NOT implement :unspecific. Some indeed don't (CLISP and ABCL at least).
- I don't know the rationale for returning it from SPLIT-NAME-TYPE. I
understand that :unspecific has different behavior under merging (which is why I don't understand why it's forbidden), so it seems like one of two things should be the case:
a. if you can return NIL for clisp and ABCL, it should be possible to return NIL for all the other implementations or
b. if returning :unspecific is necessary for some implementations, shouldn't returning NIL on CLISP And ABCL fail?
I think that in practice, the parent pathname always has NIL in its type, so that there is no difference between the merged pathname having type NIL or :UNSPECIFIC.
It seems like either these pathnames are never subjected to MERGE-PATHNAMES, in which case we can just always return NIL, or they /are/ sometimes subjected to MERGE-PATHNAMES, in which case sometimes the use of NIL instead of :unspecific will cause oddities (unless the default type is always empty).
Using :UNSPECIFIC seemed like it might produce more robust code. But now that I realize the unportability, I don't care as much.
SBCL, CCL and LispWorks all pass janderson's tests just as well with either NIL or :UNSPECIFIC. Haven't counted failures in other implementations.
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