[challenge] Lazy flatten/avoiding type forward reference with map

[David Nadlinger]

On Friday, 1 November 2013 at 09:34:20 UTC, Philippe Sigaud wrote:
>> But can you think of a more simple/elegant workaround?
>>
>>
> Is a standard lazy struct range authorized?

Sure. This wasn't intended as an actual challenge, as I don't 
have a "right" answer myself (or a prize, for that matter). ;)

I just thought I'd be interested to see what the best solution we 
can find in terms of conciseness is.

David