I would like to propose that Transducers be considered for addition to the Swift core.
"Transducers are a powerful and composable way to build algorithmic transformations that you can reuse in many contexts…"
There are ways to build them w/out any language modification but they are not as efficient as alternative expressions.
Here are some example implementations to give you an idea.
I look forward to your thoughts and comments.
Transducers are Coming — Cognitect Blog <http://blog.cognitect.com/blog/2014/8/6/transducers-are-coming>