Interesting point. I hadn't considered Perl 6, I'm trying hard not to get excited about until it's a little closer to fruition.

When you say "the for will probably be translated to a given", do you mean by an automated process? Is there an intention to provide a p5top5.pl or binary? I thought that the route was to have a p5 'mode' rather than conversion?

Given all the different ways the scalar value in the for loop could be provided

for ($scalar) {...}
for (funcReturningScalar()) {..}
for ($hash{of}{some}{arbitrar}{size}{returning}{scalar}) {...}
for($$hash{returning}{refToScalar}) { ... }
# Many more
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Unless this p5top6 processor is going to act at the bytecode level, its going to have to be a fairly sophisticated piece of code to catch all the possible variations where the topicaliser of the for returns a scalar and not a list? Would it be that much more work to have it check to see if the first line inside a bareblock was local $_ = expression; which by definition must be assigning a scalar?

Thinking about this further, I'm not sure I understand though. As given is a case-type construct, converting a one-time for to a given would result in some strange code

for ($scalar) {
    # do stuff;
}
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Becoming

given ($scalar) {
    when <<always>> {
        # do stuff;
    }
}
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I'm not quite clear how you would express the always? Though I assume given will have an equivalent of C's default: clause, so I guess it could become

given ($scalar) {
    default {
        # do stuff;
    }
}
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But I'm not sure that's much better.