Re: string> missing?

[Bozhidar Batsov <bozhidar@batsov.com>]

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Way too much bikeshedding for something super trivial. Let's add the
function(s) and be done with it.

On 4 June 2015 at 08:43, Tassilo Horn <tsdh@gnu.org> wrote:

> Eli Zaretskii <eliz@gnu.org> writes:
>
> >> Emacs is inconsistent.  That's part of its inheritance.
> >> If someone wants to add string>, I'm perfectly OK with it.
> >
> > Why not _remove_ string< and use compare-strings for both jobs?
>
> Oh yes, please.  Everybody wants to use a function of 6-7 arguments! ;-)
>
> Fun aside: aside from the reason of symmertry/consistency, I can see at
> least two practical advantages of having `string>'.  Whenever it should
> be used as predicate of a higher-order function,
>
>   (sort coll #'string>)
>
> is more concise than
>
>   (sort coll (lambda (a b) (string< b a)))
>
> and it is also better to edebug because you are usually not
> interested in edebugging the lambda.  (What can possibly go wrong
> there?!?)
>
> However, this is true for any other simple predicate aside from number
> or string comparison.  So I'd suggest to have a `complement' function
> which simply returns a function negating the value of some predicate,
> e.g.,
>
> (defun complement (fn)
>   "Returns a function calling FN and returning FN's negated value."
>   (lambda (&rest args)
>     (not (apply fn args))))
>
> Then you can do
>
>   (sort coll (complement #'string<))
>
> which looks like a good compromise wrt conciseness and edebuggability.
> Of course, (complement #'string<) is string>= which will work fine for
> `sort' but probably not for other higer-order functions.
>
> Grepping the emacs source code, there are indeed at least three
> occurrences of (nreverse (sort coll predicate)) which could make use of
> that.  And I can also find occurrences of (lambda (a b) (string< b a)).
> However, when the number of definitions is what makes a function which
> is currently not provided by Elisp important, than it looks to me that
> there should be a function for
>
>   (lambda (a b) (string< (car a) (car b)))
>
> For that, `rgrep' delivers 40 matches in the elisp repositories I have
> on my disk, and I only searched for
>
>   "(lambda (. .) (string< (car .) (car .)))"
>
> so it has to occur on one line with the exact spacing and 1-char wide
> arguments.  So that suggests we want to have a
> `car-string-less-than-car' (or indeed want to have the numerical
> comparison functions work for strings, too, as Stefan suggested because
> there's already `car-less-than-car').
>
> Bye,
> Tassilo
>
>

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