Re: RFC 165: Allow variables in a tr///

[Mark-Jason Dominus]

> One thing to be careful of there is thread safety.  You can't hand
> the data off the syntax node (the one with the tr op on it), because
> tr/$foo/$bar/ wouldn't work for several threads in it at the same
> time then.

Certainly, but that is true for everything else that is in the op
node, which includes the pattern in m/.../o.  

One of my hopes is that the Perl 6 internals will fix this
long-standing error, in which case the solution they adopt will apply
to tr///e in the same way that it will to m//o and ?? and X...Y
and all the rest.