I have a couple of questions regarding C< :: > in perl 6 rules.
First, a question of verification -- in
$rule = rx :w / plane :: (\d+) | train :: (\w+) | auto :: (\S+) / ;
"travel by plane jet train tgv today" ~~ $rule
I think the match should fail outright, as opposed to matching "train tgv".
In other words, it acts as though one had written
$rule = rx :w / plane ::: (\d+) | train ::: (\w+) | auto ::: (\S+) / ;
and not
$rule = rx :w /[ plane :: (\d+) | train :: (\w+) | auto :: (\S+) ]/ ;
Does this sound right?
Next on my list, S05 says "It is illegal to use :: outside of
an alternation", but A05 has
/[:w::foo bar]/
which leads me to believe that :: isn't illegal here even though there's
no alternation. I'd like to strike that sentence from S05.
Also, A05 proposes incorrect alternatives to the above
/[:w[]foo bar]/ # null pattern illegal, use <null>
/[:w()foo bar]/ # null capture illegal, and probably undesirable
/[:w\bfoo bar]/ # not exactly the same as above
I'd like to remove those from A05, or at least put an "Update:"
note there that doesn't lead people astray. One option not
mentioned in A05 that we can add there is
/[:w<?null>foo bar]/
which is admittedly ugly.
So, now then, on to the item that got me here in the first place.
The upshot of all of the above is that
rx :w /foo bar/
is not equivalent to
rx /:w::foo bar/
which may surprise a few people. The :: at the beginning of
the pattern effectively anchors the match to the beginning of
the string or the current position -- i.e., it eliminates the
implicit C< .*? > at the start of the match. To put the :w
inside the rule (e.g., in a variable or subrule), one would
have to write it as
rx /[:w::foo bar]/
rx /:w<null>foo bar/
Now then, I don't have a problem at all with this outcome --
but I wanted to let p6l verify my interpretation of things and
make sure it's okay for me to adjust S05/A05 accordingly.
Pm
