In Perl 6, we apply those constraints when you pass off the call to the
ultimate recipient, and that's important because that recipient can have
multiple signatures (and signatures can be added *after* you define the
flip).
For example:
$ cat foo.p6
sub flip(&f) { -> $b, $a, |c { f($a, $b, |c) } }
multi sub counter(Int $start, Int $end, :$by=1) {
$start, *+$by ... $end
}
multi sub counter(Str $start, Str $end, :$by=1) {
($start.ord, *+$by ... $end.ord).map: {.chr}
}
my &flip-counter = flip &counter;
say flip-counter 10, 2, :by(2);
say flip-counter 'q', 'k', :by(2);
say flip-counter 3.7, 1, :by(2);
$ perl6 foo.p6
(2 4 6 8 10)
(k m o q)
Cannot resolve caller counter(Int, Rat, Int); none of these signatures
match:
(Int $start, Int $end, :$by = 1)
(Str $start, Str $end, :$by = 1)
in block <unit> at foo.p6 line 3
Aaron Sherman, M.:
P: 617-440-4332 Google Talk, Email and Google Plus: a...@ajs.com
Toolsmith, developer, gamer and life-long student.
On Thu, Sep 8, 2016 at 2:41 PM, Trey Harris <t...@lopsa.org> wrote:
> On Thu, Sep 8, 2016 at 9:23 AM Aaron Sherman a...@ajs.com
> <http://mailto:a...@ajs.com> wrote:
>
> I don't know Haskell, but isn't flip just:
>>
>> sub flip(&f) { -> $b, $a, |c { f($a, $b, |c) } }
>>
>> And then:
>>
>> perl6 -e 'sub flip(&f) { -> $a, $b, |c { f($b, $a, |c) } }; my &yas =
>> flip &say; yas(1,2,3)'
>> 213
>>
>> Yes—but my worry about that was that it wouldn’t carry over signature
> constraints and coercions as a specific argument-flipper sub written with
> the same signature (flipped). Haskell does deep type inference, unlike Perl
> 6, so simply writing flip f x y = f y x is sufficient to get exactly the
> same behavior in constrained or coercive contexts.
>
>
>> Aaron Sherman, M.:
>> P: 617-440-4332 Google Talk, Email and Google Plus: a...@ajs.com
>> Toolsmith, developer, gamer and life-long student.
>>
>>
>> On Wed, Sep 7, 2016 at 6:13 PM, Brandon Allbery <allber...@gmail.com>
>> wrote:
>>
>>> On Wed, Sep 7, 2016 at 6:08 PM, Parrot Raiser <1parr...@gmail.com>
>>> wrote:
>>>
>>>> There is a "flip" in P6, to reverse the characters in a string, and a
>>>> "reverse", to return the elements of a list. Would either of those be
>>>> an equivalent?
>>>>
>>>
>>> Not without an "apply" mechanism used for function / method / operator
>>> invocations. Which is almost viable in Perl 6 since the parameters get
>>> passed as a list --- except that the list is only visible within the
>>> implementation, not at the call site (which is what "apply" does).
>>>
>>> --
>>> brandon s allbery kf8nh sine nomine
>>> associates
>>> allber...@gmail.com
>>> ballb...@sinenomine.net
>>> unix, openafs, kerberos, infrastructure, xmonad
>>> http://sinenomine.net
>>>
>>
>>
>
