On Tue, 13 Jul 2004, Larry Wall wrote:
> On Tue, Jul 13, 2004 at 07:24:55AM -0600, Luke Palmer wrote:
> : But in Perl 6, you don't have to specify things like that through the
> : mode string: you can specify them through named parameters:
> :
> : my $fh = open ">$filename" :excl;
>
> While that probably works, I think better style would be to use a comma:
>
> my $fh = open ">$filename", :excl;
>
> That explicitly passes :excl to open as a term in a list rather
> than relying on the magical properties of :foo to find the preceding
> operator adverbially when used where an operator is expected. We may
> have to tighten up the definition of operator :foo a bit, since it's
> not always going to be clear which preceding operator is intended.
> Even quotes are operators if you squint.
[snip]
> I see several directions we could go to clarify this, and I don't
> entirely like any of them. [snip]
>
> Operator adverbs are, in essence, postfix operators with weird
> precedence. We're going to have to be very explicit about what we
> mean by "weird" here. Unfortunately, this morning I don't feel
> very explicit.
My understanding is that the :adverb is at the end because it is passed as
a named argument, which must be after the positional arguments. And that
is certainly unambiguous with the comma.
However we have a precedent in m:i// where the :adverb comes directly
after the operator. It's probably special because it "is parsed" that
way, but it's so common that I feel I can use it as a precedent anyway.
So if :adverbs are having such a weird time finding their verbs, wouldn't
it be easier to allow them to be placed directly after the verb all the
time? Then the magic is merely moving it into the named args section
instead of wondering which operator's named args section it belongs to.
Then
my $fh = open ">$filename" :excl;
is unambiguously
my $fh = open (circumfix:""('>$filename', :excl));
while what was actually wanted is written as either of
my $fh = open ">$filename", :excl; # part of the arg list
my $fh = open :excl ">$filename"; # adverb to open
And besides, I think it reads better when the adverb is next to the verb.
yes, no, maybe?
~ John Williams
