On Wed, Feb 15, 2006 at 10:09:05AM +0100, H. Stelling wrote:
> - Capture numbering:
>
> /(a) [ (b) (c) (d) | (e) & (f) ] (g)/ capture.t suggests something like
> $0 $1 $2 $3 $1 $2 $4, but I'm only guessing about the
> "&" bit.
Yes.
> In the following,
>
> / (a) [ (b) (c) | $5 := (d) $0 := (e) ] (f) /
>
> does the first alias have any effect on where the f's will go
> (probably not)?
I'll defer to @Larry on this one, but my initial impression is
that the (f) capture would go into $6.
> - Which rules do apply to repeated captures with the same alias? For
> example,
> the second array aliasing example
>
> m:w/ Mr?s? @<names> := <ident> W\. @<names> := <ident>
> | Mr?s? @<names> := <ident>
> /;
>
> seems to suggests that by using $<names>, the lower branch would have
> resulted in a single Match object instead of an array (like the array we
> would have gotten if we hadn't used the aliases in the first place). Is
> this right?
Yes, that's correct.
> And could the same effect have been achieved by something
> like
>
> / $<names> := <indent>**{1} / ?
Yes, a quantified capturing subrule or subpattern results in an
array of Match objects (even if the quantification is "1").
> - More array aliasing:
>
> is / mv @<files> := [...]* /
> just (slightly) shorter for / mv [$<files> := [...]]* / ?
I think so.
> Likewise, could / @<pairs> := ( (\w+) \: (\N+) )+ /
> have also been written / [ $<pairs> := (\w+) \: $<pairs> := (\N+) ]+ / ?
Seems like it would work.
> - Array and hash aliasing of quantified subpatterns or subrules: what
> happens
> to the named captures?
>
> / @<foo> := ( ... $bar := (...) ... )* /
Presuming you meant $<bar> there instead of $bar, I have no idea
what would happen. (With $bar it's an external alias and would
capture an array of matches into the scope in which the rule was
declared.)
> And if the subpattern or subrule ends with an alternation, can the
> number of
> array elements to be appended (or hashed) vary depending on whitch
> branch is
> taken?
Again I have to refer this to @Larry, but my initial impression is
"yes, it would vary".
> - Which of the following constructs could possibly be ok (I hope, none)?
>
> / $<foo> := ... & $<foo> := ... /
I think this one is okay. $<foo> is an array of Match objects, and
each Match is likely repeated within the array.
> / $<foo> := ... %<foo> := ... /
I hope this is not okay. It's certainly not going to be okay anytime
soon in the PGE implementation of Perl 6 rules. :-)
> / $<foo> := ... | %<foo> := ... /
Since the two aliases are in separate alternation branches, I think
this is okay. The argument would be similar to
/ $<foo> := ... | @<foo> := .../
in which $<foo> is either a single Match object or an array of
Match objects depending on the branch matched.
> / $<foo> := $<foo> := ... /
While my instinctual reaction is to say that this ought to be okay,
upon thinking about it a bit more I think I'd prefer to say that
it's not. At least initially, if nothing else. In particular, I
wonder about something like
/ @<foo> := $<bar> := [...]+ /
If we say that an alias always requires a subpattern or subrule
(and not another alias), then we avoid a lot of ambiguity, and the
above could be written as
/ @<foo> := [ $<bar> := [...]+ ] /
/ @<foo> := [ $<bar> := [...] ]+ /
depending on what is desired.
> - Do aliases bind right-to-left, as do assignments?
> / $2 := $5 := ... / # next should be $3, not $6
Assuming we allow chained aliases such as this (see above note),
I'd still argue for $6 instead of $3.
> - Which kind of escape sequences are allowed (or required) in enumerated
> character classes?
AFAIK, this hasn't been completely decided or specified yet.
Pm
