Add parens around pretty printing of application

[mattpolzin]

It's been really fun to explore Dhall via Idris interop so thanks for putting this library together!

I found that pretty printing almost created valid Dhall if I had e.g. an Optional List of Naturals, but it lacked parentheses. This PR over-applies parentheses so that the result is always valid Dhall even if sometimes it has more parentheses than needed.

before:

Optional List Text

after:

Optional (List Text)

[alexhumphreys]

Thanks for all the changes! I'm a bit out of the loop on idris at the moment unfortunately (got a reminder to check once a week for issues/PRs here), but if you're planning on making more changes I'd be happy to add you as a collaborator. As long as the tests are passing you could merge your own PRs 👍

Speaking of, the tests are failing on this one, but I think it's just a matter of adding parenthesis on line 5, 13, 14, 15 here. After that it should be good to go

[mattpolzin]

@alexhumphreys If you want to give me merge privvies I won’t argue! I do try very hard not to abuse such things, so I wouldn’t merge anything that fell outside of “better support the dhall spec” without waiting for your input anyway.

[alexhumphreys]

Sounds good, just invited you there 🙌