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# Emacs {#sec-emacs}
## Configuring Emacs {#sec-emacs-config}
The Emacs package comes with some extra helpers to make it easier to configure. `emacs.pkgs.withPackages` allows you to manage packages from ELPA. This means that you will not have to install that packages from within Emacs. For instance, if you wanted to use `company` `counsel`, `flycheck`, `ivy`, `magit`, `projectile`, and `use-package` you could use this as a `~/.config/nixpkgs/config.nix` override:
```nix
{
packageOverrides = pkgs: with pkgs; {
myEmacs = emacs.pkgs.withPackages (epkgs: (with epkgs.melpaStablePackages; [
company
counsel
flycheck
ivy
magit
projectile
use-package
]));
}
}
```
You can install it like any other packages via `nix-env -iA myEmacs`. However, this will only install those packages. It will not `configure` them for us. To do this, we need to provide a configuration file. Luckily, it is possible to do this from within Nix! By modifying the above example, we can make Emacs load a custom config file. The key is to create a package that provide a `default.el` file in `/share/emacs/site-start/`. Emacs knows to load this file automatically when it starts.
```nix
{
packageOverrides = pkgs: with pkgs; rec {
myEmacsConfig = writeText "default.el" ''
;; initialize package
(require 'package)
(package-initialize 'noactivate)
(eval-when-compile
(require 'use-package))
;; load some packages
(use-package company
:bind ("<C-tab>" . company-complete)
:diminish company-mode
:commands (company-mode global-company-mode)
:defer 1
:config
(global-company-mode))
(use-package counsel
:commands (counsel-descbinds)
:bind (([remap execute-extended-command] . counsel-M-x)
("C-x C-f" . counsel-find-file)
("C-c g" . counsel-git)
("C-c j" . counsel-git-grep)
("C-c k" . counsel-ag)
("C-x l" . counsel-locate)
("M-y" . counsel-yank-pop)))
(use-package flycheck
:defer 2
:config (global-flycheck-mode))
(use-package ivy
:defer 1
:bind (("C-c C-r" . ivy-resume)
("C-x C-b" . ivy-switch-buffer)
:map ivy-minibuffer-map
("C-j" . ivy-call))
:diminish ivy-mode
:commands ivy-mode
:config
(ivy-mode 1))
(use-package magit
:defer
:if (executable-find "git")
:bind (("C-x g" . magit-status)
("C-x G" . magit-dispatch-popup))
:init
(setq magit-completing-read-function 'ivy-completing-read))
(use-package projectile
:commands projectile-mode
:bind-keymap ("C-c p" . projectile-command-map)
:defer 5
:config
(projectile-global-mode))
'';
myEmacs = emacs.pkgs.withPackages (epkgs: (with epkgs.melpaStablePackages; [
(runCommand "default.el" {} ''
mkdir -p $out/share/emacs/site-lisp
cp ${myEmacsConfig} $out/share/emacs/site-lisp/default.el
'')
company
counsel
flycheck
ivy
magit
projectile
use-package
]));
};
}
```
This provides a fairly full Emacs start file. It will load in addition to the user's presonal config. You can always disable it by passing `-q` to the Emacs command.
Sometimes `emacs.pkgs.withPackages` is not enough, as this package set has some priorities imposed on packages (with the lowest priority assigned to Melpa Unstable, and the highest for packages manually defined in `pkgs/top-level/emacs-packages.nix`). But you can't control this priorities when some package is installed as a dependency. You can override it on per-package-basis, providing all the required dependencies manually - but it's tedious and there is always a possibility that an unwanted dependency will sneak in through some other package. To completely override such a package you can use `overrideScope'`.
```nix
overrides = self: super: rec {
haskell-mode = self.melpaPackages.haskell-mode;
...
};
((emacsPackagesFor emacs).overrideScope' overrides).withPackages
(p: with p; [
# here both these package will use haskell-mode of our own choice
ghc-mod
dante
])
```
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