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Re: Strange interaction between pairs and named binding

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From:
Autrijus Tang
Date:
July 18, 2005 21:25
Subject:
Re: Strange interaction between pairs and named binding
Message ID:
20050719042502.GA97843@aut.dyndns.org
On Mon, Jul 18, 2005 at 03:48:55PM -0700, Brent 'Dax' Royal-Gordon wrote:
> Autrijus Tang <autrijus@autrijus.org> wrote:
> > This currently works in Pugs:
> >
> >     for [1..10].pairs -> Pair $x { say $x.value }
> >
> > But this does not:
> >
> >     for [1..10].pairs -> $x { say $x.value }
> >
> > Because the ruling that pairs must not be bound to parameters that are
> > not explicitly declared to handle them.  Is this a desirable behaviour?
> 
> How much violence would be done to the language if we declared that
> block (i.e. closure with no "sub" keyword) parameters defaulted to
> Item|Pair, while sub parameters defaulted to plain Item?  I can't
> imagine named arguments are going to be used very often on blocks,
> which tend to be things like loop bodies...

If the Bare code object (including pointy and non-pointy) default their
parameter types to "Any" (that is, Item|Pair|Junction), then all of
these would work:

    for [1..10].pairs { say(.value) }
    for [1..10].pairs { say($^x.value) }
    for [1..10].pairs -> $x { say($x.value) }
    for 1|2, 3|4 { say(.values) }
    for 1|2, 3|4 { say($^x.values) }
    for 1|2, 3|4 -> $x { say($x.values) }

> Right now one of my biggest Perl 6 nits is that the combination of
> subroutines everywhere and the Pair type's special role in subroutine
> dispatch makes Pairs a real pain to work with.  This would help to fix
> the problem without creating a new SuperPair type or something
> similarly silly.

Seconded.

Thanks,
/Autrijus/


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