User blog comment:Vel!/Ellipsis considered harmful/@comment-27394924-20170605172751/@comment-30754445-20170605183720

Well, it is possible. It's just very unwieldy:

Define a sequence of character strings as follows:

c(0)="1"

c(n+1)=concatenate("0,", c(n-1)")

Then:

a[0{1}1]b = a[c(b)]a

Quite cumbersome, but it works.