Internal and external iteration, fibers

[Rob T]

On Friday, 18 January 2013 at 17:59:36 UTC, Nick Sabalausky wrote:
> Fibers: Too much performance overhead to be a general solution. 
> Only
> good for, as an example, heavily I/O-bound stuff.

Where does the overhead come from? Is the overhead from using 
fibers the only problem for implementing coroutines?

I ask, because if except for the overhead, fibers are a good 
general solution, then it makes sense to determine if anything 
can be done to lessen the overhead before trying to implement yet 
another solution.

--rt