General-purpose keymap management à-la Emacs.

nkeymaps

#+TITLE: NKeymaps
#+SUBTITLE: General-purpose keymap management

This keymap library is inspired by [[https://savannah.nongnu.org/projects/emacsy][Emacsy]] (=keymap.scm=), which in turn is
inspired by Emacs.

The main types are:

- A =key= structure has a hardware =code=, a symbolic =value=, an ordered set of
  modifiers (the order is to avoid inequality on permutation) and possibly more
  in the future.

  Whitespaces are the only reserved characters.  Anything else can be stored in
  the =key= value.

- A =keyspec= is a string representation of a =key=.  A =keyspec= is a
  space-separated string representation of a sequence of =key=s.

- A =keymap= contains a hash-table where the keys are a =keyspec= and the values
  are either a keymap or anything else.  As a special case, a =nil= value
  unbinds the key.

** Goals

- Support prefix keys to other keymaps.  For instance, prefixing my-mode-map
  with =C-c= makes all bindings for my-mode accessible after pressing =C-c=.
- List all bindings matching a given prefix.  (Also known as =which-key= in
  Emacs.)
- List the bindings associated to a command.
- Support multiple inheritance.
- Support keycode.
- Validate keyspec at compile time.
- ~define-key~ can set multiple bindings in a single call.
- Support multiple keyschemes to make it easy to switch between, say, Emacs-style
  and VI-style bindings.  This orthogonality to keymaps composes better than
  having multiple keymaps: changing keyscheme applies to the entire program, which
  is easier than looping through all keymaps to change them.
- Translate keyspecs as a fallback.  For instance if =shift-a= is unbound, check
  =A=.
- Customizable behaviour with global parameters such as ~*print-shortcut*~.
- The ~compose~ function can merge multiple keymaps together.
- Support multiple arguments when that makes sense (e.g. multiple keymaps for
  ~lookup-key~).
- Key remapping à-la Emacs.
- Typed keymaps, i.e. keymaps where bound values can only be of a given type.
  This is convenient to catch typos, for instance when binding ='FOO= instead of
  =#'FOO=.

** Non-goals

- Customizable modifiers: the input system must decide how to map =meta=,
  =control=, etc.
- Dead key support: the input system must handle it.
- Fallback function when binding is not found: the caller of =lookup-key= gets
  =nil= when unbound, thus it can decide of a default behaviour.
- Provide a self-insert function: the caller must handle it.
- Global or local bindings: it's up to the calling application to manage the
  locality of their keymaps.

** Example

#+begin_src lisp
  (let* ((parent-keymap (nkeymaps:make-keymap "parent-keymap"))
         (my-keymap (nkeymaps:make-keymap "my-keymap" parent-keymap)))
    (nkeymaps:define-key parent-keymap
      "C-c" 'copy
      "C-v" 'paste)
    (nkeymaps:define-key my-keymap
      "C-x" 'cut)
    (values
     (nkeymaps:lookup-key "C-x" parent-keymap)
     (nkeymaps:lookup-key "C-x" my-keymap)
     (nkeymaps:lookup-key "C-c" my-keymap)))

  ;; => NIL, CUT, COPY
#+end_src

See the [[file:package.lisp][package]] documentation for a usage guide and more examples.

** History

NKeymaps was originally developed for keymap management in [[https://nyxt.atlas.engineer][Nyxt]], so the "N"
may stand for it, or "New", or whatever poetic meaning you may find behind it!

** Road-map

- [ ] Lookup order (for instance parent-first or next-keymap-first) should be customizable.

- [ ] For now =*translator*= is a global, but ideally it would be part of the
  keyscheme and keymap.  But this would impact the lookup order, since
  translations come after all the keymaps and their parents have been searched for.

** Change log

*** 1.0.0

- Renamed =scheme-name= to =keyscheme= and =scheme= to =keyscheme-map=.
  It's more consistent and intuitive.  The previous naming was really confusing.
- All warnings have now their own conditions, see the =nkeymaps/conditions= package.
- =define-keyscheme-map= has a different syntax, it's now
  #+begin_src lisp
    (define-keyscheme-map "NAME-PREFIX" (:import OPTIONAL-KEYSCHEME-MAP-TO-IMPORT)
      KEYSCHEME BINDINGS...)
  #+end_src
- The predefined =keyscheme=s are now accessible from the =nkeymaps= package.
- New =default= =keyscheme= which is the new parent of other keyschemes
  (including =cua=), instead of =cua=.
- =*modifier-list*= is no longer exported.  Instead, both =keyscheme= and
  =keymap= have a =modifiers= slot for the modifiers they accept.
- Switched testing framework from =Prove= to =Lisp-Unit2=.
- Removed the =cl-str= dependency.


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