Two new Hydra colors - pink and teal

Two new colors are being added up to a total of five: red, blue, amaranth, pink and teal. I should carefully restate what they do to avoid confusion.

The three rules of Hydratics

1. A hydra may not injure a human being or, through inaction, allow a human being to come to harm.

Seriously though, see below.

Rule 1: Hydra heads are either red or blue

Once you're in a Hydra state:

• calling a red head will call the command and continue the state
• calling a blue head will call the command and stop the state

They may have a reddish or a bluish face that isn't exactly red or blue, but that's what they are underneath. I hope you get what I mean.

Rule 2: red or blue is inherited from the body color

This is merely a convenience, you can still explicitly override each head to be blue or red:

• if the body is red, amaranth or pink, the heads inherit red
• if the body is blue or teal, the heads inherit blue

Rule 3:

When you call a binding which isn't a head:

• amaranth, teal and pink Hydras will intercept it
• red and blue Hydras will quit and let Emacs execute your binding

Finally, on intercepting a non-head, amaranth and teal will issue a warning and do nothing without quitting. And pink will try to call the intercepted command without quitting. Currently only non-prefix bindings can be called, since I haven't figured out how to do it for prefixes.

A nice table to sum things up

Thanks to @kaushalmodi for pointing me in this direction:

|----------+-----------+-----------------------+-----------------|
| Body     | Head      | Executing NON-HEADS   | Executing HEADS |
| Color    | Inherited |                       |                 |
|          | Color     |                       |                 |
|----------+-----------+-----------------------+-----------------|
| amaranth | red       | Disallow and Continue | Continue        |
| teal     | blue      | Disallow and Continue | Quit            |
| pink     | red       | Allow and Continue    | Continue        |
| red      | red       | Allow and Quit        | Continue        |
| blue     | blue      | Allow and Quit        | Quit            |
|----------+-----------+-----------------------+-----------------|

The extra-awesome Ruby-style Hydra docstrings

Turns out learning Ruby wasn't a complete waste of time, at least I learned about string interpolation. And now I'm sticking it into Elisp packages, first tiny, and now hydra.

How it works:

(defhydra hydra-toggle (:color pink)
  "
_a_ abbrev-mode:       %`abbrev-mode
_d_ debug-on-error:    %`debug-on-error
_f_ auto-fill-mode:    %`auto-fill-function
_g_ golden-ratio-mode: %`golden-ratio-mode
_t_ truncate-lines:    %`truncate-lines
_w_ whitespace-mode:   %`whitespace-mode

"
  ("a" abbrev-mode nil)
  ("d" toggle-debug-on-error nil)
  ("f" auto-fill-mode nil)
  ("g" golden-ratio-mode nil)
  ("t" toggle-truncate-lines nil)
  ("w" whitespace-mode nil)
  ("q" nil "cancel"))

(global-set-key (kbd "C-c C-v") 'hydra-toggle/body)

Here, using e.g. "_a_" translates to "a" with proper face. More interestingly, e.g.

"foobar %`abbrev-mode"

translates roughly to

(format "foobar %S" abbrev-mode)

This means that you actually see the state of the mode that you're changing. The escape syntax was chosen with another intent in mind: because of the backquote, if you have company-mode on, you can complete the symbols while in string.

See how it looks like in action:

Small note on pink Hydras

It's useful for instance it the above example, when I don't care about self-inserting, but I still want to do navigation. Basically pink Hydra is the closest thing to an actual minor mode. Thanks to @angelic-sedition for the idea.

Small note on teal Hydras

It provides an interface similar to magit dispatch: pressing appropriate keys does things and pressing the wrong keys issues a warning. The only difference between teal and amaranth is the color inheritance, otherwise they behave exactly the same. This means that if you want a non-quitting Hydra that will end up with more blue heads, start with teal, otherwise, start with amaranth. Thanks to @ffevotte for the idea.

Outro

It feels like things are finally falling into place with this package. I hope that you like the new changes and find new cool uses for the added abilities. Happy hacking!