Hi Paul.
There is a statement that Arrows can be used as streaming approach. Arrows are very new for me, so my question may looks stupid, but would somebody show me clean and simple example how it will look? Lets suppose we have function `getLines` which returns `IO [String]`, a lot of lines :) And I want to process them as I do it with streaming library (or pipes) - with constant space.
If it's true, then I can use Arrows instead of pipes, right?
No. Or rather maybe. But mostly no. Arrows are just a particular way to write and think about code. You can structure a library to be particularly well suited to arrows, but what a library does and how you use it is completely orthogonal. When people say arrows are suitable for a streaming approach, what they often mean is that thinking in terms of arrows and thinking in terms of streams are compatible. That means that no amount of arrows will help you stream your data. And if you use a streaming library that's optimised for arrows, you can forego the arrows if you want. In fact arrows have fallen out of favour with most Haskell programmers because (1) you can get almost all their advantages with just Applicatives and (2) many things Arrow syntax would be great for can't be implemented with how the Arrow hierarchy is currently structured and desugared. For that reason I don't think any modern streaming library will rely on arrows. That being said, to help you with the need for streams, might I point you to the excellent conduit-library. It's a bit complex to learn, but their github (https://github.com/snoyberg/conduit) has a rather impressive introduction. Cheers, MarLinn