On Wed, Feb 17, 2016 at 09:07:42AM -0700, Sandra Loosemore wrote:
> On 02/17/2016 12:14 AM, Tom de Vries wrote:
> >
> >Here's the documentation entry for the gt spec function (I forgot to add
> >it when introducing the function), using the new semantics.
> >
> >Copy-pasting from the resulting .info viewed in emacs for a
> >human-readable version:
> >...
> > 'gt'
> > The 'gt' (greater than) function takes one or more arguments.
> > It returns either NULL or the empty string. If it has one
> > argument, it returns NULL. If it has two arguments, it
> > compares them: it returns the empty string if the first
> > argument is greater than the second argument, otherwise it
> > returns NULL. If it has more than two arguments, it behaves
> > as if only the last two arguments were passed. It can be used
> > f.i. as 'S' in a spec directive %{'S':'X'}: if 'S' is NULL,
> > the empty string is substituted, and if 'S' is the empty
> > string, 'X' is substituted.
> >
> > %:gt(%{fsome-option-value=*:%*} 1)
> >...
> >
> >OK for stage4 trunk?
>
> I'm not an expert on spec strings.... but from a user perspective, what is
> the difference between "NULL" and "the empty string"? The other spec
> escapes are documented in terms of pattern substitutions at the point where
> the escape appears in the spec string.
NULL vs. "" is the internal (C level representation) of %:fn() function
returned false vs. true for the purpose of e.g. %{%:fn():...}.
Jakub
