Which are more than just the permission bits, adding set user and group ID, and the "sticky" bit to restrict deletion in directories such as /tmp. POSIX offers 15 of these in http://pubs.opengroup.org/onlinepubs/9699919799/basedefs/sys_stat.h.html, but rwx AKA 7 for usr, group, and others are gratuitous, can be achieved by anding the 3 individual read, write and execute bitmasks. Then again, this is the POSIX API....

The rationale is that we shouldn't require users to know 4/2/1 AKA rwx and their combinations, and the user, group, and other ordering, instead we can tell them to use these masks through importing a bitwise operator SRFI like 151.

On the other hand, this could reasonably be the remit of the library I've postulated that would also offer fancier symbolic specification of these bits, and return an integer permission bits mask to hand to the various procedures that take it. On the third hand, for standardization in usage we should think about including such a library in this SRFI, there's a design we can use for it in 0.7 scsh, which as previously discussed put it at too low a level and didn't retain the option of supplying the simple bitmask.

BTW, while implementing the file-info-directory? etc. set of predicates for Chibi Scheme, I noticed that POSIX of course distinguishes between block and character special files, scsh only offers file-info-special? etc., so I made the appropriate changes to the specification and Implementation sections, swapping the latter for the two specific ones.