Early return from iterators is not supported

[emil14]

In imperative programming you can stop iteration by using break or return keywords, but in Nevalang's dataflow it's not possible - for, map, filter, etc will process the whole stream even if its infinite. How do we solve this problem?

1. Implement Iterator protocol (early termination for stream processing for both parent and child) #666 and use it for all iterators? Wouldn't that be hard to use?
2. Make existing iterators send -> :err to signal stop? Is it popular usecase enough to make using more complicated (in theory you could just not write to :err outport)
3. Introduce other components for this usecase (e.g. While)?

[emil14]

:err outport problem

In Go you if err != nil and return err inside for loop, in Nevalang you can't do anything if inside handler of your for/map/flter/etc you got :err from somewhere. You basically can't use ? operator too

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Maybe #724 can be used for loop too?