That will depend on how the Perl 6 parser works. If it pre-tokenizes (like Perl 5 does) then we shall almost certainly still have a "longest interpretation possible" tokenizing rule. So:

$x = $y //foo/;

will have to be interpreted as:

$x = $y // foo/;

But if (as I hope) we tokenize on-the-fly, then the parser will be able to backtrack this incorrect interpretation and re-parse it as:

$x = $y / /foo/;

instead.

Indeed, if that is the parsing strategy, the issue here would never even arise, since the higher precedence of / over // would see that interpretation considered first. (Of course, there would be backtracking when compiling:

$x = $y //foo;

in that case, since the higher precedence interpretation doesn't work.)

Personally, I think JIT tokenization will be the only feasible approach for Perl 6, given how mutable the language will be (e.g. user-defined operators).

And, almost as a happy by-product, that is likely to inject the maximum degree of DWIMity into the language.

Damian