Simple exercise

[Rick Johnson]

On Monday, March 14, 2016 at 10:17:54 AM UTC-5, Ian wrote:
> It's sometimes very useful [for zip to discard values],
> though. 

The obvious solution is to allow the caller to decide if the
error should be raised, or not. Currently, the caller has no
control over the internals of zip unless he creates a
wrapper, or validates the sequences by hand, before passing 
them into zip. Both of which are violating DRY.