Add orthogonal edges feature.

[kindaro]

Closes #42.

[kindaro]

Here is how it looks on the module Test.Reference:

[jonascarpay]

How does this interact with --no-splines? Might it make sense to have a three-way flag/toggle Spline | Straight | Ortho?

[kindaro]

Good question… I had not thought this through.

It does make sense to have a three-way toggle! Let me fix this.

[kindaro]

Three-way toggle installed!

[jonascarpay]

Ah, I think we should probably write the parser similar to this: https://github.com/jonascarpay/calligraphy/blob/master/src/Calligraphy.hs#L166-L171, that way, the CLI will automatically document the possible flags. Does that make sense or was there a particular reason you did it this way?

[kindaro]

This is a deep question.

In the ideal world, optparse-applicative would give us a way to say «parse this sum type» and automatically generate help text. But it does not.

I do not think adding a bunch of mutually exclusive flags is the right approach, because generally the expectation is that separate flags can be set independently from one another. When we want to telegraph that several flags are mutually exclusive, we make an option instead.

What I am doing is a common approach. Here is an example of a ReadM parser from ormolu, defined the same way as my parser here. When they define the option, they enumerate all the possible values by hand.

That said, I can do it your way as well. It is up to you to decide!

[jonascarpay]

I agree neither way is ideal. Let's stick to your way, but then please add the accepted values to the help text and/or the error message

[kindaro]

I added the accepted values to the help text and to the error message.

[jonascarpay]

LGTM!

[kindaro]

I forgot to update the change log… See #51.