Re: concat([])

[Jack Brennen <jfb@brennen.net>]

I don't necessarily disagree, just pointing out the ambiguity in the
usage.  I just looked through my own directory of GP programs (of my
own authorship) and found that out of 107 usages of concat(),
I almost exclusively use the two-argument form -- concat(A,B) --
and that if I expect a string return value, I seem to
explicitly use Str() on at least one of the two arguments rather than
depending on implicit type recognition.

I suppose that's indicative of my own long experience with GP and
how to get predictable results, although I've never really thought
a lot about it (until now).

Note that concat([],[]) returns [] as expected, and that
concat("","") returns "" as expected.


On 7/7/2014 5:14 PM, Max Alekseyev wrote:
> Hi Jack,
>
> I believe the general purpose of concat() is to concatenate vectors,
> while strings are viewed as a special type of vectors (of characters).
> > From this perspective, the default type of concat result is 'vector',
> unless it is specifically asked to concatenate strings (in which case
> result type is 'string').
> That's why I think concat([]) should not be much different from
>
> ? concat([[]])
> %3 = []
>
> Regards,
> Max
>
>
> On Mon, Jul 7, 2014 at 7:23 PM, Jack Brennen <jfb@brennen.net> wrote:
> > Or should it be "" ?
> >
> > "ab" <- concat(["a","b"])
> > "a"  <- concat(["a"])
> > ""   <- concat([])
> >
> > I guess it's ambiguous, so it is rejected?
> >
> > Note that concat() has some serious weirdnesses
> > when you mix strings with other types...
> > This is version 2.5.5 behavior:
> >
> > ? concat(["",1,x,y])
> > %1 = "1xy"
> > ? concat([1,x,y,""])
> > %2 = "[1, x, y]"
> > ? concat([[],x,y,""])
> > %3 = "[x, y]"
> > ? concat([[],x,y,[]])
> > %4 = [x, y]
> > ? concat(["",x,y,[]])
> > %5 = "xy[]"
> >
> > It seems as if it progresses using non-string-based concatenation
> > until it finds a string, at which point it converts the result
> > so far to a string and then continues?
> >
> >
> >
> >
> >
> > On 7/7/2014 3:34 PM, Max Alekseyev wrote:
> > > ? concat([])
> > >     ***   at top-level: concat([])
> > >     ***                 ^----------
> > >     *** concat: domain error in concat: vector = []
> > >     ***   Break loop: type 'break' to go back to GP prompt
> > >
> > >
> > > Should it simply return [] ?
> > >
> > > Regards,
> > > Max