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Introduction

eta a micro-framework for customising key-bindings built on top of bind-key. It provides two macros for standardising and associating intent with key-bindings: a standard version eta-bind and multi-dispatch version for standardisation of functionality across major modes: eta-modal-init and eta-modal.

Installation

Install from Melpa:

quepa

(use-package eta :ensure t)

Usage

Let’s see these macros in action:

eta-bind

;; First argument is a [vector]
;; [*] means cannot be overriden
;; [] means global but can be overriden by other modes
;; [<keymap>] means bind for given mode only

;; Subsequent arguments are tabular of the form
;; - ACTION   (a tag that states what the action is)
;; - BINDINGS (a set of key bindings bound to the intent)
;; - IMPLEMENTATION (the actual command that performs the action)

;;  ACTION          BINDINGS                    IMPLEMENTATION
(eta-bind [*]        
  ::no-action       ()                          'e/no-action                  ;; can be nothing
  ::which-key       ("C-x C-h" "C-x h")         'which-key-show-major-mode    ;; allow multi
  ::main-menu       ("C-p" "M-p" "M-x" "ESC p" "ESC x")   'counsel-M-x
  ::quit            ("ESC q" "M-q")             'save-buffers-kill-terminal
  ::help-key        ("ESC <f1>")                'helpful-key
  ::eval-elisp      ("ESC l")                   'eval-last-sexp)

eta-modal

It’s easier to think of this as using multimethods for major modes. eta-modal-init is akin to defmulti while eta-modal is akin to defmethod. This allows actiovs that will be consistent across major modes.

For example the default bindings in Eclipse are <F8> for build and <F6> for debug. Build and Debug are actions that can be reassigned key-bindings. Whether one is writing java, c++ or any other language, these actions are the same although the underlying implementation might be very different.

This type of standardisation can now be applied to one’s Emacs setup.

;; ACTION              BINDINGS              INTERACTIVE PARAMS
(eta-modal-init []
  ::mode-menu          ("<f8>")              ()
  ::eval-cursor        ("C-e")               ("P")
  ::eval-cursor-alt    ("C-x p" "C-x C-p")   ("P")
  ::eval-file          ("C-x x" "C-x C-x")   ())
  
;;... then later on ...

;; elisp mode
(eta-modal [::lisp   lisp-interaction-mode]
  ::eval-cursor     'eval-last-sexp
  ::eval-file       'e/eval-buffer
  ::eval-cursor-alt 'pp-macroexpand-last-sexp)

;; org mode
(eta-modal [::org    org-mode]
  ::eval-cursor     'org-ctrl-c-ctrl-c
  ::eval-cursor-alt 'e/org-babel-tangle-block
  ::mode-connect    'org-babel-tangle
  ::eval-file       nil)

;; elisp mode
(eta-modal [::clojure  cider-mode]
  ::eval-cursor     'cider-eval-last-sexp
  ::eval-file       'cider-eval-buffer
  ::eval-cursor-alt 'cider-macroexpand-last-sexp)
  
;; ... and so on ...

Concept

eta provides a indirection layer between the bindings and the implementation so that the intent of the user can be stated.

BINDINGS -> [ACTION or INTENT] -> IMPLEMENTATION

This leads to better organisation a cleaner binding definition and gives the user a bit more control over where the bindings are placed. It makes migrating away from older libraries much less painful.

Another features is the ability to have multiple keybindings for a given action. This is extremely useful in a lot of situations:

  • allow access to a commonly used feature at various hand positions
  • when minor modes override one binding, the feature is still available via another set of shortcuts.

Similar Libraries

These are current libraries that attempt to solve the same problem:

  • Bind Key is the go to binding library shipped as part of use-package. eta is essentially offerring a more conventient interface for bind-key).
  • Major Mode Hydra is a multimethod for only the one action. In this case, a user can define a major-mode-hydra key that brings up the hydra menu for the mode.
    • This library is backed by pretty-hydra. pretty-hydra and eta are used extensively in etude for modal menus (effectively emulatinig what Major Mode Hydra provides).
  • General does something similar.
  • Rigpa This project is quite recent, very interesting and offers a framework for the user to build around as opposed to eta’s whatever goes approach.