Add primitives for arrows

[rpglover64]

They are commonly used and annoying to construct manually.

A stop-gap measure could be to add documentation detailing how to construct them, but I think that would be more work than actually adding the primitives.

I try to view diagrams as a competitor with tikz, and I find it disappointing that tikz wins here by such a large margin.

[byorgey]

Thanks for opening this ticket! We've long known this is a huge missing feature and are actively working towards it. e.g. see #71, and some notes on the wiki here: http://www.haskell.org/haskellwiki/Diagrams/Dev/Arrows . I want to "do it right" and there are some tricky issues to consider.

[rpglover64]

I do appreciate the "do it right" mentality, and I am unsurprised that there is active dev work (I'll check it out soon), but I was surprised at a lack of an issue; I didn't find the wiki page, so hopefully this report will make it easier to find for people in the future.

[byorgey]

I agree! Hence my thanks for the ticket. =)

[rpglover64]

And thank you for developing and maintaining the library :)

[byorgey]

Note this is currently being worked on in the arrows branch, https://github.com/diagrams/diagrams-lib/tree/arrows . Right now we are aiming to include this in the 0.7.1 release.

[jeffreyrosenbluth]

should this issue be closed ?

[byorgey]

Yes! Closing via @26b7fdf .