On Mon, 02 Oct 2017 00:26:27 -0700, alex.jakime...@gmail.com wrote:
> Oh. Maybe it's https://rt.perl.org/Ticket/Display.html?id=127279 ?
>
> On 2017-08-26 08:01:06, alex.jakime...@gmail.com wrote:
> > Indeed, I'm not sure what I was smoking.
> > On 2017-01-20 21:27:50, sml...@gmail.com wrote:
> > > > It numifies ranges so that the number of elements is used. In other
> > > > words, 1..2
> > > > works like 2 and 1..1 works like 1.
> > >
> > > No, if it worked like that then the first two examples would throw the
> > > same error as the third, instead of exhibiting behaviors that are both
> > > different from that and from each other.
> > >
> > > Here are two more examples, showing the difference in case of an
> > > actual arithmetic series:
> > >
> > > ➜ say 1..1, 3 ... 7;
> > > (1..1 3 4 5 6 7)
> > >
> > > ➜ say 1, 3 ... 7;
> > > (1 3 5 7)
This may be operating as designed.
First, note that in ..., you are not guaranteed that all the elements in the
first list are returned:
$ perl6 -e 'say 1,2,3,4...3'
(1 2 3)
...as soon as the 3 on the lhs matches the 3 on the rhs, the sequence
terminates.
And yes, some of this is due to ranges collapsing to +.elems. The comparison to
the first value of the rhs list is a smart match, to wit:
$ perl6 -e 'say (4..7) ~~ 4'
True
$ perl6 -e 'say (4..8) ~~ 4'
False
..only a 4-element list smartmatches 4.
So for the above examples here is what is happening:
1..2,7,5...2; # 1..2 matches 2. Emit it and stop.
1..1,7,5...2; # nothing matches the 2. So we follow the spec...
where we fall under the "they do not look like numbers" clause,
since the range is not a simple number (as an aside, note that
((1..1) - 7) is (6..6))
So we skip doing this:
"That is, supposing we call the last three numbers C<$a>, C<$b>, and
C<$c>, and then define:
$ab = $b - $a;
$bc = $c - $b;
If C<$ab == $bc> and C<$ab> is not zero, then we deduce an arithmetic
progression determined by the function C<*+$ab>. If C<$ab> is zero,
and the three values look like numbers, then the function is C<*+0>."
...and we do this instead:
"If they do not look like numbers, then the function selected is either
C<*.succ> or C<*.pred> depending on whether C<$b cmp $c> appears to be
Increasing or Decreasing. If C<cmp> returns Same then an identity
function is assumed."
...$b is 7 and $c is 5, so we call .pred on 5 until we get a result that
matches 2.
1,7,5...2; # We have three actual trailing numbers and should be able to deduce
a pattern, but cannot.
