I went down that path so that the leaf case could use the bare block syntax like a map.

And I can see your point as well. You already have a wrapper function however. If the underlying implementation used a hash of callbacks then you could provide the neater codeblock style as well as the clunkier but more powerful hash of callbacks style as well. Everybody wins then.

Maybe die "cut" could be an appropriate out of band return value.

Yep, I can see that working nicely.

Cheers,