Double hmmm.... That would also supplant the lone '*' wart in indexing
syntax: instead of saying
@array[0..10;*;@x]
you could say
@array[0..10; !; @x]
Presumably, the '!;' would expand to the scalar undef value, which could be
interpreted as "do nothing on this axis", while in the related construct
@a=();
@array[0..10; @a; @x]
the '@a;' would instead expand to a list ref pointing to the empty list, which
could be interpreted instead as "return the null set" -- minimizing surprise
if @a is only occasionally empty.
(Of course, substitute your favorite postfix unary character instead of '!';
'*' would work just as well...)
Quoth Craig DeForest on Monday 10 January 2005 03:56 pm,
> Hmmmm... It would be easy to distinguish the slicing cases if it were
> easier to distinguish between a number and a list containing just [In
> fact, that is more or less how perl5/PDL's arg-list-based slicer ('mslice')
> does things.]
>
> At the top of Synopsis 9, there's a discussion about exactly that:
> > @array[0..10; 42; @x]
> >is really short for
> > @array.postcircumfix:<[ ]>( <== [0..10], [42], [EMAIL PROTECTED] );
> >though in the list of lists form, a bare number is interpreted as if it
> > were a list of one element, so you can also say:
> > @array.postcircumfix:<[ ]>( <== [0..10], 42, [EMAIL PROTECTED] );
>
> I believe that this is Wrong, because the distinction that is being blurred
> turns out to be important. Ideally, those two postcircumfix cases should
> do different things (slice versus index).
>
> But you can have your cake and eat it too. If those postcircumfix cases
> were really different, one could take advantage of the still-unused postfix
> unary '!' (for example) to distinguish:
> @array[0..10; 42!; @x] [[ maps to ]] (<== [0..10], 42 , [EMAIL
> PROTECTED] );
> @array[0..10; 42; @x] [[ maps to ]] (<== [0..10], [42], [EMAIL
> PROTECTED] );
>
> Then the default behavior is consistent (semicolons denote lists of lists)
> but there is an "escape hatch" that lets you make a list of
> scalars-and-lists.
>
>
>
>
> Quoth Larry Wall on Monday 10 January 2005 11:04 am,
>
> > On Sat, Jan 08, 2005 at 11:37:06AM -0700, Craig DeForest wrote:
> > : I just re-read Synopsis 9, which covers PDL-related actions and array
> > : slicing, and came to the conclusion that either (A) there's a hole in
> > : the syntax as it is lain out, (B) I lack sufficient understanding of
> > : what has been thought out so far, or (C) that part of the language
> > : definition isn't finished yet.
> >
> > I expect C is closest to the mark. :-)
> >
> > : Is the perl6 expression
> > : @a[4; 0..5];
> > : a 1x6 array (probably correct)? Or a 6 array (probably not correct)?
> >
> > Certainly the former. I don't think dimensions should ever disappear
> > accidentally.
> >
> > : If the former, how do you specify that you want the latter?
> >
> > I don't know offhand. I see both the lure and the danger of the
> > extra parens, so we'll probably not go that route. We could find
> > some keyword that destroys the current dimension while supplying a
> > scalar argument:
> >
> > @a[gone(4); 0..5];
> >
> > Or maybe we want some notation that is explicitly a null slice with
> > a scalar value, maybe something like:
> >
> > @a[() but 4; 0..5];
> >
> > or
> >
> > @a[():pick(4); 0..5];
> >
> > or
> >
> > @a[4 but dim(); 0..5];
> >
> > or maybe even something strange like:
> >
> > @a[()=4; 0..5];
> >
> > But I'm certainly open to other suggestions.
> >
> > Larry
