Re: RFC PATCH: Sketch at :@ subscripting

[Lawrence Velázquez <vq@xxxxxxxxx>]

On Sat, Mar 27, 2021, at 4:27 PM, Bart Schaefer wrote:
> On Sat, Dec 19, 2020 at 1:13 AM Stephane Chazelas <stephane@xxxxxxxxxxxx> wrote:
> >
> > 2020-12-18 14:18:15 +0100, Mikael Magnusson:
> > [...]
> > > The idea is that you can do this:
> > > % typeset -a somearray=( 'data here' 'some words' etc etc 1 2 3 4 ) idx=(1 3 5)
> > > % echo ${somearray:@idx}
> > > data here etc 1
> > [...]
> >
> > Hi Mikael,
> >
> > I can't help but think that allowing to specify the indexes
> > directly as perl does for instance in:
> >
> > print @list[1, 4, 2, 7..10, @idx, -1];
> 
> The way to do this (syntactically speaking) would be with a subscript
> flag.  E.g.:
>   print $array[(^)1,3,7]
> would change the interpretation of the commas to select a set of
> elements instead of a range.  I chose (^) because of symmetry with
> $^array and to avoid confusion with for example $array[@].
> 
> I haven't looked into how difficult that might be to implement,
> particularly in assignment context.
> 
> Another possibility is to handle $array[{1,3,7}] specially since "{"
> is already a syntax error in math context.
> 
> Both of those options could apply to associative arrays, although keys
>  would need to respect quoting to avoid troubles with an embedded ",".
> 
> >   $ i=1,3
> >   $ echo ${a[i]}
> >   c
> 
> Here [i] is interpreted in math context so the comma becomes an
> operator (the collision you already noted) so this becomes $a[3]
> 
> >   $ echo ${a[$i]}
> >   a
> 
> This one is confusing and a bug ... it should be the same as
> ${a[$[$i]]} but instead it's ${a[,3]}.  I haven't tracked down exactly
> what's skipping everything up to but not including the first comma (it
> is not, for example, just dropping one character).

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