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
