@main[]

$demo[
    $.a[1]
    $.b[2]
    $.c[3]
    $.d[4]
]

1. ^rename[v;c]
   ^rename[b;b]
2. ^rename[b;x]
   ^rename[a;x]
   ^rename[d;x]
3. ^rename[a;c]
   ^rename[d;a]
   ^rename[b;c]

4. ^rename[ $.a[b] $.b[c] $.c[d] ]
   ^rename[ $.a[a1] $.b[b1] $.c[c1] ]

5. ^rename[a;]
   ^rename[b;$void]
   ^rename[ $.a[] $.b[] $.c[] ]

6. ^try-catch{ ^demo.rename[a] }
   ^try-catch{ ^demo.rename{a}[b] }
   ^try-catch{ ^demo.rename[a]{b} }
   ^try-catch{ ^demo.rename[$.a[b];c] }

@rename[a;b]
$h[^hash::create[$demo]]
^if($a is hash){
    ^h.rename[$a]
}{
    ^h.rename[$a;$b]
}
$result[^json:string[$h]]