On Tue, Dec 12, 2017 at 4:49 PM Stefan Monnier <monnier@iro.umontreal.ca>
wrote:

> I tend to think of Hydra as "bindings that stick around" (to take the
> wording on the first line of hydra.el), rather than "ways to show
> available bindings of the current submap".  So, yes, I think it does
> something else (something more)


Well, that's correct ..

than what I understand you want.
>

Though I now think I did a very bad job at constructing that problem
statement. But I know for sure that hydra.el fits the bill perfectly (I've
been using it ever since Oleh released it).

Integrating hydra into emacs with help package developers do these:
- Create interfaces for transitional keymaps
- The bindings could be sticky or not (can be configured in hydra)
- Allow customizing the descriptions of the bindings (@JWiegley as you
later suggest which-key, which-key does not allow that.. well it does.. but
the user will need to tweak the description, etc.. I see which-end more as
a tool only for the end-user. hydra can be used both by package developers
and end users).
- Pick and choose which bindings to "show" in that interface.. you don't
have to show all. The package developer may choose to have duplicate
bindings for some function in that keymap, but prefer to show only the
preferred binding in the hydra popup (cannot do that in which-key.. it
shows *everything*).


> And, BTW, if I take a hydra like
>
>     (defhydra hydra-zoom (global-map "<f6>")
>       "zoom"
>        ("g" text-scale-increase "in")
>        ("l" text-scale-decrease "out"))
>
> and I press `f6` I don't get any help in the echo area (nor in the "lv"
> area).  I only get that help after pressing `f6 g` or `f6 l`, so I need
> some other mechanism to find those "initial" key bindings.
>

That's because you used Style 1 (as explained in this hydra Wiki:
https://github.com/abo-abo/hydra/wiki/Binding-Styles). Use the Style 2 to
take care of the issue you stated:

(defhydra hydra-zoom ()
  "zoom"
  ("g" text-scale-increase "in")
  ("l" text-scale-decrease "out"))

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

In Style 1, you allow the hydra to share the "keymap space" with other
bindings not related to that hydra.

In Style 2, the hydra takes over the whole "keymap space". In above Style 2
example, the "C-c" space is completely ruled by the hydra-zoom hydra.


> So in this respect, I think it does something less than what
> I understand you'd want.
>

No. It does everything that I need to do. But of course it has a lot of
features, which might be suitable for different applications. See keys like
:pre, :post and more described in
https://github.com/abo-abo/hydra/wiki/internals.

I can see something like this begin added to smerge.el if and when hydra.el
gets merged to the core (See the use of :pre and :post):

(defhydra hydra-smerge (:color pink
                        :hint nil
                        :pre (smerge-mode 1)
                        ;; Disable `smerge-mode' when quitting hydra if
                        ;; no merge conflicts remain.
                        :post (smerge-auto-leave))
  "
^Move^       ^Keep^               ^Diff^                 ^Other^
^^-----------^^-------------------^^---------------------^^-------
_n_ext       _b_ase               _<_: upper/base        _C_ombine
_p_rev       _u_pper              _=_: upper/lower       _r_esolve
^^           _l_ower              _>_: base/lower        _k_ill current
^^           _a_ll                _R_efine
^^           _RET_: current       _E_diff
"
  ("n" smerge-next)
  ("p" smerge-prev)
  ("b" smerge-keep-base)
  ("u" smerge-keep-upper)
  ("l" smerge-keep-lower)
  ("a" smerge-keep-all)
  ("RET" smerge-keep-current)
  ("\C-m" smerge-keep-current)
  ("<" smerge-diff-base-upper)
  ("=" smerge-diff-upper-lower)
  (">" smerge-diff-base-lower)
  ("R" smerge-refine)
  ("E" smerge-ediff)
  ("C" smerge-combine-with-next)
  ("r" smerge-resolve)
  ("k" smerge-kill-current)
  ("q" nil "cancel" :color blue))


> > I quickly went though hydra.el.. isn't defhydra mainly what it is? What
> > would you suggest splitting out of that library?
>
> I don't know enough about it to have a clear opinion on that.
>

OK.

Thanks.
-- 

Kaushal Modi