#+TITLE: Emacs Lisp layer

#+TAGS: dsl|layer|lisp|programming

[[file:img/emacs.png]]

* Table of Contents                     :TOC_5_gh:noexport:
- [[#description][Description]]
  - [[#features][Features:]]
- [[#install][Install]]
- [[#auto-compile][Auto-compile]]
- [[#working-with-lisp-files-barfage-slurpage--more][Working with lisp files (barfage, slurpage & more)]]
- [[#debugging-elisp][Debugging Elisp]]
  - [[#using-the-inspector][Using the inspector]]
- [[#nameless][Nameless]]
  - [[#aliases][Aliases]]
- [[#structurally-safe-editing][Structurally safe editing]]
- [[#key-bindings][Key bindings]]
  - [[#additional-testing-functions-with-overseer][Additional testing functions with overseer]]
  - [[#additional-evaluation-functions][Additional evaluation functions]]
  - [[#format-code][Format code]]
  - [[#debugging][Debugging]]
  - [[#refactoring-with-emr][Refactoring with emr]]
  - [[#inspector][Inspector]]

* Description
This layer gathers all the configuration related to emacs-lisp. This should
always be in your dotfile, it is not recommended to uninstall it.

** Features:
- Auto-completion using company
- Linting using flycheck integration
- Linting package file metadata using [[https://github.com/purcell/flycheck-package][flycheck-package]]
- Repl support via =IELM=
- Support for specific lisp navigation styles via =emacs-lisp-mode=
- Auto-compile via [[https://github.com/tarsius/auto-compile][auto-compile]] package
- Debugging via [[https://www.gnu.org/software/emacs/manual/html_node/elisp/Edebug.html#Edebug][edebug]]
- Ert test runner with [[https://github.com/tonini/overseer.el][overseer]]
- Nameless package prefix with optional [[https://github.com/Malabarba/Nameless][nameless]]
- Structurally safe editing using optional [[https://github.com/luxbock/evil-cleverparens][evil-cleverparens]]
- Visual feedback when evaluation using [[https://github.com/hchbaw/eval-sexp-fu.el][eval-sexp-fu]]

* Install
To use this configuration layer, add it to your =~/.spacemacs=. You will need to
add =emacs-lisp= to the existing =dotspacemacs-configuration-layers= list in this
file.

* Auto-compile
This layer adds the [[https://github.com/tarsius/auto-compile][auto-compile]] package to automatically keep the byte-compiled
version of your Emacs lisp files synced with the uncompiled version on every
save. If there are any compiler errors in the file, you will see a counter show
up in the mode line. You can hover over these numbers to get a description or
view the compiler output with the ~SPC m c l~ key binding. To disable the
feature use this line in your =dotspacemacs/user-config= function.

#+BEGIN_SRC emacs-lisp
  (remove-hook 'emacs-lisp-mode-hook 'auto-compile-mode)
#+END_SRC

You can also exclude the =auto-compile= package.

* Working with lisp files (barfage, slurpage & more)
Spacemacs comes with a special =lisp-state= for working with lisp code that
supports slurpage, barfage and more tools you'll likely want when working with
lisp.

As this state works the same for all files, the documentation is in global
[[https://github.com/syl20bnr/spacemacs/blob/master/doc/DOCUMENTATION.org#lisp-key-bindings][DOCUMENTATION.org]]. In general, use ~SPC k~ to interact with the lisp-state.

* Debugging Elisp
Here is an interactive quick start to debug Emacs Lisp from an =emacs-lisp-mode= buffer.

To follow this tutorial open the code of the following source block in an
=emacs-lisp-mode= buffer. One way to do this is to first find this emacs-lisp
layer documentation file in Spacemacs using ~SPC h l emacs-lisp RET~. This will
open the current file in =space-doc-mode=. Toggle off =space-doc-mode= using =,
T V= so that Spacemacs will switch to =org-mode=. Now you can place the cursor
somewhere inside the code block and press ~, '~ to open the code in an
interactive =emacs-lisp-buffer=. 

#+BEGIN_SRC elisp
  (defun helloworld (name)
    (let ((n (subroutine name)))
      (message (format "Hello world, %s!" name))))

  (defun subroutine (s)
    (concat "my dear " s))

  (helloworld "Spacemacs")
#+END_SRC

Steps:
Now from within the =emacs-lisp-buffer=
1) Evaluate each sexp by putting your point in each of them and press ~, e f~ or
   press ~, e b~ to evaluate all code in the buffer at once.
2) To debug the =helloworld= function, put your cursor on the =defun= keyword and

press ~SPC m d f~ (or ~, d f~), it will put a breakpoint on the function (we say
that we instrumentalise this function) so whenever the Lisp interpreter
encounters this function it will start the debugger.
3) Then go to the closing parenthesis of =(helloworld "Spacemacs")= and press

~, e e~ to evaluate it, if you are using =vim= editing style you end up in
evilified state otherwise you end up in emacs state and =*Debugging*= is
displayed in the mode line.
4) Press ~s~ to go to next step up to the opening parenthesis of
   =(subroutine name)=,
5) Press ~i~ to go into the =subroutine= where you can press ~s~ to step in

function or press ~o~ to go out of it.
6) Press ~a~ to stop debugging.

** Using the inspector
This layer adds the [[https://github.com/mmontone/emacs-inspector][inspector]] package to provide an easy way for inspecting
data structures. Find more information about its usage [[https://github.com/mmontone/emacs-inspector][here]] and see key bindings.

* Nameless
Nameless hides package namespaces in your emacs-lisp code, and replaces it by
leading ~>~ It can be toggled with ~SPC m T n~.

By default =nameless= is deactivated, to enable it set the layer variable
=emacs-lisp-hide-namespace-prefix= to =t=.

NOTE: =nameless= is known to cause problems when spacemacs is used inside a
terminal window, use with caution.

#+BEGIN_SRC emacs-lisp
  (setq-default dotspacemacs-configuration-layers '(
    (emacs-lisp :variables emacs-lisp-hide-namespace-prefix t)))
#+END_SRC

** Aliases
This layer defines some global aliases for Spacemacs:

| alias | namespace           |
|-------+---------------------|
| .S    | dotspacemacs        |
| CL    | configuration-layer |
| S     | spacemacs           |
| SB    | spacemacs-buffer    |

You can define additional alias in function =dotspacemacs/user-config= of your
dotfile:

#+BEGIN_SRC emacs-lisp
  (add-to-list 'nameless-global-aliases '("N" . "nameless"))
#+END_SRC

* Structurally safe editing
This layer adds support for =evil-cleverparens= which allows to safely edit
lisp code by keeping the s-expressions balanced.

By default this mode is not activated. You can turn it on locally on the active
buffer with ~SPC m T s~ (=s= for safe).

To turn it on automatically for all =emacs-lisp= buffers call the following
function in your =dotspacemacs/user-config= function:

#+BEGIN_SRC emacs-lisp
  (spacemacs/toggle-evil-safe-lisp-structural-editing-on-register-hook-emacs-lisp-mode)
#+END_SRC

or to enable it for all supported modes:

#+BEGIN_SRC emacs-lisp
  (spacemacs/toggle-evil-safe-lisp-structural-editing-on-register-hooks)
#+END_SRC

When enabled the symbol =🆂= should be displayed in the mode-line.

* Key bindings

| Key binding                | Description                                            |
|----------------------------+--------------------------------------------------------|
| ~SPC m g g~                | go to definition of symbol under point                 |
| ~SPC m g G~                | go to definition of symbol under point in other window |
| ~SPC m h h~                | describe symbol at point                               |
| ~SPC m c c~                | byte compile the current file                          |
| ~SPC m c l~                | popup compile-log buffer                               |
| ~SPC m e $~ or ~SPC m e l~ | go to end of current line and evaluate                 |
| ~SPC m e b~                | evaluate current buffer                                |
| ~SPC m e C~                | evaluate current =defun= or =setq=                     |
| ~SPC m e e~                | evaluate sexp before point                             |
| ~SPC m e f~                | evaluation current function                            |
| ~SPC m e r~                | evaluate current region                                |
| ~SPC m ​,​~                  | toggle =lisp state=                                    |
| ~SPC m t b~                | run tests of current buffer                            |
| ~SPC m t q~                | run =ert=                                              |
| ~SPC m d m~                | open [[https://github.com/joddie/macrostep][macrostep]] transient-state                         |
| ~SPC m :~                  | toggle nameless minor mode                             |

** Additional testing functions with overseer
Function related to test are present under the ~SPC m t~ prefix:

| Key binding | Description   |
|-------------+---------------|
| ~SPC m t a~ | overseer test |
| ~SPC m t A~ | test debug    |
| ~SPC m t t~ | run test      |
| ~SPC m t b~ | test buffer   |
| ~SPC m t f~ | test file     |
| ~SPC m t g~ | test tags     |
| ~SPC m t p~ | test prompt   |
| ~SPC m t q~ | test quiet    |
| ~SPC m t h~ | test help     |

** Additional evaluation functions
If =smartparens= is used the following additional key bindings are available:

| Key binding | Description                  |
|-------------+------------------------------|
| ~SPC m e c~ | evaluate sexp around point   |
| ~SPC m e s~ | evaluate symbol around point |

** Format code
The [[https://github.com/syl20bnr/spacemacs/blob/develop/layers/%2Bemacs/semantic/README.org][semantic]] layer should be installed for these key bindings to become active.

| Key binding | Description             |
|-------------+-------------------------|
| ~SPC m = b~ | format current buffer   |
| ~SPC m = d~ | format current function |
| ~SPC m = o~ | format all on one line  |
| ~SPC m = s~ | format current sexp     |

** Debugging
To start debugging:

| Key binding | Description                                                            |
|-------------+------------------------------------------------------------------------|
| ~SPC m d f~ | on a =defun= symbol toggle on the instrumentalisation of the function  |
| ~SPC m d F~ | on a =defun= symbol toggle off the instrumentalisation of the function |
| ~SPC m d t~ | insert =(debug)= to print the stack trace and re-evaluate the function |

In =edebug-mode= (=*Debugging*= is displayed in the minor modes segment of the
mode line)

| Key binding | Description                |
|-------------+----------------------------|
| ~s~         | step                       |
| ~i~         | step in                    |
| ~o~         | step out                   |
| ~S~         | next                       |
| ~f~         | forward-sexp               |
| ~H~         | goto here                  |
| ~I~         | instrument callee          |
| ~c~         | go                         |
| ~C~         | fast continue              |
| ~t~         | trace                      |
| ~T~         | fast trace                 |
| ~q~         | quit                       |
| ~Q~         | quit nonstop               |
| ~a~         | stop                       |
| ~b~         | set breakpoint             |
| ~u~         | unset breakpoint           |
| ~B~         | next breakpoint            |
| ~x~         | set conditional breakpoint |
| ~r~         | previous result            |
| ~e~         | evaluate expression        |
| ~C-x C-e~   | evaluate last sexp         |
| ~w~         | where                      |
| ~?~         | help                       |
| ~d~         | backtrace                  |

In =edebug-eval-mode=

| Key binding | Description                  |
|-------------+------------------------------|
| ~SPC m g w~ | where                        |
| ~SPC m a~   | delete evaluation item       |
| ~SPC m k~   | delete evaluation item       |
| ~SPC m ,~   | update evaluation list       |
| ~SPC m c~   | update evaluation list       |
| ~SPC m e e~ | evaluate last sexp           |
| ~SPC m e E~ | evaluate last sexp and print |

In =debugger-mode= (=Debugger= is displayed in major mode segment of the mode
line)

| Key binding | Description              |
|-------------+--------------------------|
| ~<tab>~     | forward                  |
| ~S-<tab>~   | backward                 |
| ~RET~       | backtrace help follow    |
| ~p~         | backtrace backward frame |
| ~c~         | continue                 |
| ~R~         | record expression        |
| ~d~         | step through             |
| ~e~         | eval expression          |
| ~J~         | jump                     |
| ~L~         | list functions           |
| ~b~         | frame                    |
| ~r~         | return value             |
| ~u~         | frame clear              |
| ~C-v~       | backtrace toggle locals  |
| ~q~         | quit                     |

** Refactoring with emr

| Key binding   | Description               |
|---------------+---------------------------|
| ~SPC m r f e~ | implement function        |
| ~SPC m r f d~ | find unused definitions   |
| ~SPC m r e f~ | extract function          |
| ~SPC m r e v~ | extract variable          |
| ~SPC m r e l~ | extract to let            |
| ~SPC m r e c~ | extract constant          |
| ~SPC m r e a~ | extract autoload          |
| ~SPC m r i v~ | inline variable           |
| ~SPC m r i s~ | inline let variable       |
| ~SPC m r i f~ | inline function           |
| ~SPC m r i a~ | insert autoload directive |
| ~SPC m r d l~ | delete let binding form   |
| ~SPC m r d d~ | delete unused definition  |
| ~SPC m e w~   | eval and replace          |

** Inspector
*inspector buffer*

| Key binding | Description                 |
|-------------+-----------------------------|
| ~RET~       | inspect object              |
| ~L~         | navigate to previous object |
| ~q~         | quit inspector              |

*backtrace buffer*

| ~i~ | inspect object |
