Dave Whipp wrote: > Carl Mäsak wrote: >> Paul (>): >>> I can't find anything in the existing synopses about Blobs. >>> Probably looking in the wrong place, sorry. >> >> <http://perlcabal.org/syn/S02.html#line_912> > > Re-reading that, a slightly tangent (though still on topic, I hope) > thought come to mind. The definition of the Mapping immutable type: > > Mapping Set of Pairs with no duplicate keys > > The question is, what to do when a Mapping is created from a > source that contains pairs with duplicate keys? The Perl5 answer is > simply to silently drop all but the last in the list ... but I can think > of many other answers: sometimes you might want an error; other times > you might want to create a list/set/bag from the values of the duplicate > keys; other times a junction might be appropriate. One theme of P6 is to > not lose information unnecessarily -- which is what P5 does here.
It would be nice indeed if there were a simple syntax for specifying that. OTOH it's not hard to do it manually in two lines or so. > The option of creating a list of the values is interesting because, in > scalar context, a list returns the value of its last item That's Perl 5 semantics, not Perl 6. In Perl 6 a List in scalar context becomes a List or Array object: $ ./perl6 -e 'my $x = 1, 2, 3; say $x.perl' [1, 2, 3] > -- which is > the existing P5 semantics but without losing information until the value > is used as a scalar. And lists can be used to construct all the other > interesting cases. > > Will there be a syntax for choosing the strategy for reducing a list of > pairs that contains duplicate keys to a "Mapping"? Moritz
