Re: master 71783e9: Add the string-numeric-lessp function

[Paul Eggert <eggert@cs.ucla.edu>]

Lars Ingebrigtsen wrote:

> I don't think that's something our numerical string comparison function
> should be doing.

Again, I'm not sure I'm following. The two strings "2.21-0ubuntu4" and 
"2.21-0ubuntu4.1" are identical except the latter has ".1" appended. Shouldn't 
almost any sane kind of string comparison consider the shorter to be less than 
the longer?

If only some strings are valid for comparison, I suppose the comparison function 
could be a partial function, e.g., it could signal an error when given a string 
that it doesn't think has a valid format. This of course could be done, but it 
makes usage more complicated. For sorting, having comparison functions be total 
functions is much simpler to explain.

At least, that's been the tradition in other GNU tools. GNU ls -v applies the 
string-version-lessp algorithm to every pair of file names that it considers, 
and it works on arbitrary file names. It sounds like you may be thinking of some 
other tradition, although I'm not sure what that tradition would be.

The GNU ls -v approach works well in practice, because people who care about 
version numbers tend to name their files consistently. E.g., they do not put 
files "foo001.png" "foo1.png" in the same directory, because that kind of usage 
would confuse humans no matter what 'ls -v' does.