Use render to implement an instance for Show

[L7R7]

This is a first, naive solution for #12. (less naive than just putting an orphan instance in Burrito.Internal.Render).

Baiscally I just moved the two functions in Burrito.Internal.Render that had a dependency to Burrito.Internal.Type.Template over to Burrito.Internal.Type.Template and fixed compile errors. The tests are green, and show does what I would expect.

I'm not entirely convinced that this is a good solution. In terms of cohesion, the functions I moved should reside in Render. I just moved them over to avoid the cyclic dependency.

What do you think about this?

[tfausak]

Thanks, this looks great!

All else being equal I would definitely prefer to keep all the stuff related to rendering in the render module. But I think this approach is the least of all evils. It's definitely better than orphan instances or .hs-boot files 😄

[tfausak]

I think we could keep exporting this as a type-restricted version of show.

[L7R7]

Hmm, I don't think I got that. Could you explain that a little? What is the advantage of having render in addition of show?

Apart from that, I would just have to add render to the exports of Burrito.Internal.Type.Template to get what we want, right?

[tfausak]

One advantage is API stability. Since Burrito.render currently exists, I would like to keep it there unless there's a compelling reason to remove it.

In general I like to have monomorphic versions of polymorphic functions since they can sometimes help with type inference. In this particular case it doesn't matter much since Burrito doesn't expose any polymorphic ways to create templates. But imagine if it implemented a Read instance; then you could use render . read to round-trip a template. The alternative would be something like show @Template . read or show . (\ t -> t :: Template) . read.

[L7R7]

That makes sense, thank you for the explanation! Should be done in the latest commit
Edit I'll fix the unnecessary whitespace changes as soon as I'm back at my laptop

[L7R7]

I don't even know what .hs-boot files are 😅

Apart from the open suggestion with the export for render, is there anything you'd like to see in this PR?

[tfausak]

Fantastic! This should make playing around with templates in GHCi a much nicer experience. Thank you!

One tiny little change: Could you keep the export list in the same order as before? The order in the code is the order that things show up in the documentation. I like showing parse, then render, then expand.

[tfausak]

Thank you!