# Expanding snippets

- Intro and tutorial
- Howto: organize
- Howto: expand
- Howto: write
- Howto: menu
- FAQ
- ChangeLog
- Download

Contents

- Triggering expansion
  - Trigger key
    - Fallback bahaviour
  - Insert at point
  - Snippet keybinding
  - Expanding from the menu
  - Expanding with `hippie-expand`
  - Expanding from emacs-lisp code
- Controlling expansion
  - Eligible snippets
  - The condition system
  - Multiples snippet with the same key
    - Use the X window system
    - Use built-in Emacs selection methods
    - Use `dropdown-menu.el`
    - Roll your own
- Customizable Variables
  - `yas/prompt-functions`
  - `yas/fallback-behavior`
  - `yas/choose-keys-first`
  - `yas/choose-tables-first`
  - `yas/key-syntaxes`

# Triggering expansion

You can use YASnippet to expand snippets in different ways:

- By typing a snippet abbrev and then pressing the key defined in `yas/trigger-key` (which defaults to "TAB"). This works in a buffer where the minor mode `yas/minor-mode` is active;
- By invoking the command `yas/insert-snippet` (either by typing `M-x yas/insert-snippet` or its keybinding). This does not require `yas/minor-mode` to be active.
- By using the keybinding associated with an active snippet. This also requires `yas/minor-mode` to be active;
- By expanding directly from the "YASnippet" menu in the menu-bar
- By using hippie-expand
- Expanding from emacs-lisp code

## Trigger key

When `yas/minor-mode` is enabled, the keybinding taken from `yas/trigger-key` will take effect.

`yas/trigger-key` invokes `yas/expand`, which tries to expand a snippet abbrev (also known as snippet key) before point.

The default key is `"TAB"`, however, you can freely set it to some other key.

To enable the YASnippet minor mode in all buffers globally use the command `yas/global-mode`.

When you use `yas/global-mode` you can also selectively disable YASnippet in some buffers by setting the buffer-local variable `yas/dont-active` in the buffer's mode hook.

Trouble when using or understanding the `yas/trigger-key` is easily the most controversial issue in YASsnippet. See the FAQ.

### Fallback bahaviour

`yas/fallback-behaviour` is a customization variable bound to `'call-other-command` by default. If `yas/expand` failed to find any suitable snippet to expand, it will disable the minor mode temporarily and find if there's any other command bound the `yas/trigger-key`.

If found, the command will be called. Usually this works very well -- when there's a snippet, expand it, otherwise, call whatever command originally bind to the trigger key.

However, you can change this behavior by customizing the `yas/fallback-behavior` variable. If you set this variable to `'return-nil`, it will return `nil` instead of trying to call the original command when no snippet is found.

## Insert at point

The command `M-x yas/insert-snippet` lets you insert snippets at point for you current major mode. It prompts you for the snippet key first, and then for a snippet template if more than one template exists for the same key.

The list presented contains the snippets that can be inserted at point, according to the condition system. If you want to see all applicable snippets for the major mode, prefix this command with `C-u`.

The prompting methods used are again controlled by `yas/prompt-functions`.

## Snippet keybinding

See the section of the `# binding:` directive in Writing Snippets.

## Expanding from the menu

See the YASnippet Menu.

## Expanding with `hippie-expand`

To integrate with `hippie-expand`, just put `yas/hippie-try-expand` in `hippie-expand-try-functions-list`. This probably makes more sense when placed at the top of the list, but it can be put anywhere you prefer.

## Expanding from emacs-lisp code

Sometimes you might want to expand a snippet directly by calling a functin from elisp code. You should call `yas/expand-snippet` instead of `yas/expand` in this case.

As with expanding from the menubar, condition system and multiple candidates won't exists here. In fact, expanding from menubar has the same effect of evaluating the follow code:

    (yas/expand-snippet template)

See the internal documentation on `yas/expand-snippet` for more information.

# Controlling expansion

## Eligible snippets

YASnippet does quite a bit of filtering to find out which snippets are eligible for expanding at point.

In particular, the following things matter:

- Currently loaded snippets tables

  These are loaded from a directory hierarchy in your file system. See Organizing Snippets. They are named after major modes like `html-mode`, `ruby-mode`, etc...

- Major mode of the current buffer

  If it matches one of the loaded snippet tables, then all that table's snippets are considered for expansion. Use `M-x describe-variable RET major-mode RET` to find out which mode you are in currently.

- Parent tables

  Snippet tables defined as parent of some other table considered in the previous step are also considered.

- Buffer-local `yas/mode-symbol` variable

  This can be used to consider snippet tables whose name does not correspond to a major mode. If you set this variable to a name , like `rinari-minor-mode`, you can have some snippets expand only in that minor mode. Naturally, you want to set this conditionally, i.e. only when entering that minor mode, using a hook is a good idea.

    ;; When entering rinari-minor-mode, consider also the snippets in the
    ;; snippet table "rails-mode"
    (add-hook 'rinari-minor-mode-hook
              #'(lambda ()
                  (setq yas/mode-symbol 'rails-mode)))

- Buffer-local `yas/buffer-local-condition` variable

  This variable provides more fine grained control over what snippets can be expanded in the current buffer. The default value, won't let you expand snippets inside comments or string literals for example. See The condition system for more info.

## The condition system

Consider this scenario: you are an old Emacs hacker. You like the abbrev-way and set `yas/trigger-key` to `"SPC"`. However, you don't want `if` to be expanded as a snippet when you are typing in a comment block or a string (e.g. in `python-mode`).

If you use the `# condition :` directive (see Writing Snippets) you could just specify the condition for `if` to be `(not (python-in-string/comment))`. But how about `while`, `for`, etc. ? Writing the same condition for all the snippets is just boring. So has a buffer local variable `yas/buffer-local-condition`. You can set this variable to `(not (python-in-string/comment))` in `python-mode-hook`.

Then, what if you really want some particular snippet to expand even inside a comment? This is also possible! But let's stop telling the story and look at the rules:

- If `yas/buffer-local-condition` evaluate to nil, no snippets will be considered for expansion.
- If it evaluates to the a cons cell where the `car` is the symbol `require-snippet-condition` and the `cdr` is a symbol (let's call it `requirement`), then:
  - Snippets having no `# condition:` directive won't be considered;
  - Snippets with conditions that evaluate to nil (or produce an error) won't be considered;
  - If the snippet has a condition that evaluates to non-nil (let's call it `result`):
    - If `requirement` is `t`, the snippet is ready to be expanded;
    - If `requirement` is `eq` to `result`, the snippet is ready to be expanded;
    - Otherwise the snippet won't be considered.
- If it evaluates to the symbol `always`, all snippets are considered for expansion, regardless of any conditions.
- If it evaluate to `t` or some other non-nil value:
  - If the snippet has no condition, or has a condition that evaluate to non-nil, it is ready to be expanded.
  - Otherwise, it won't be considered.

In the mentioned scenario, set `yas/buffer-local-condition` like this

    (add-hook 'python-mode-hook
              '(lambda ()
                 (setq yas/buffer-local-condition
                       '(if (python-in-string/comment)
                            '(require-snippet-condition . force-in-comment)
                          t))))

... and specify the condition for a snippet that you're going to expand in comment to be evaluated to the symbol `force-in-comment`. Then it can be expanded as you expected, while other snippets like `if` still can't expanded in comment.

## Multiples snippet with the same key

The rules outlined above can return more than one snippet to be expanded at point.

When there are multiple candidates, YASnippet will let you select one. The UI for selecting multiple candidate can be customized. A customization variable, called `yas/prompt-functions` defines your preferred method of being prompted for snippets.

You can customize it with `M-x customize-variable RET yas/prompt-functions RET`. Alternatively you can put in your emacs-file:

    (setq yas/prompt-functions '(yas/x-prompt yas/dropdown-prompt))

Currently there are some alternatives solution with YASnippet.

### Use the X window system

The function `yas/x-prompt` can be used to show a popup menu for you to select. This menu will be part of you native window system widget, which means:

- It usually looks beautiful. E.g. when you compile Emacs with gtk support, this menu will be rendered with your gtk theme.
- Emacs have little control over it. E.g. you can't use `C-n`, `C-p` to navigate.
- This function can't be used when in a terminal.

### Use built-in Emacs selection methods

You can use functions `yas/completing-prompt` for the classic emacs completion method or `yas/ido-prompt` for a much nicer looking method. The best way is to try it. This works in a terminal.

### Use `dropdown-menu.el`

The function `yas/dropdown-prompt` can also be placed in the `yas/prompt-functions` list.

This works in both window system and terminal and is customizable, you can use `C-n`, `C-p` to navigate, `q` to quit and even press `6` as a shortcut to select the 6th candidate.

### Roll your own

See below for the documentation on variable `yas/prompt-functions`

# Customizable Variables

## `yas/prompt-functions`

You can write a function and add it to the `yas/prompt-functions` list. These functions are called with the following arguments:

- PROMPT: A string to prompt the user;
- CHOICES: A list of strings or objects;
- optional DISPLAY-FN : A function. When applied to each of the objects in CHOICES it will return a string;

The return value of any function you put here should be one of the objects in CHOICES, properly formatted with DISPLAY-FN (if that is passed).

- To signal that your particular style of prompting is unavailable at the moment, you can also have the function return nil.
- To signal that the user quit the prompting process, you can signal `quit` with `(signal 'quit "user quit!")`

## `yas/fallback-behavior`

How to act when `yas/expand` does not expand a snippet.

`call-other-command` means try to temporarily disable YASnippet and
  call the next command bound to `yas/trigger-key`.

`return-nil` means return nil. (i.e. do nothing)

An entry (apply COMMAND . ARGS) means interactively call COMMAND, if ARGS is non-nil, call COMMAND non-interactively with ARGS as arguments.

## `yas/choose-keys-first`

If non-nil, prompt for snippet key first, then for template.

Otherwise prompts for all possible snippet names.

This affects `yas/insert-snippet` and `yas/visit-snippet-file`.

## `yas/choose-tables-first`

If non-nil, and multiple eligible snippet tables, prompts user for tables first.

Otherwise, user chooses between the merging together of all eligible tables.

This affects `yas/insert-snippet`, `yas/visit-snippet-file`

## `yas/key-syntaxes`

The default searching strategy is quite powerful. For example, in `c-mode`, `"bar"`, `"foo_bar"`, `"#foo_bar"` can all be recognized as a snippet key. Furthermore, the searching is in that order. In other words, if `"bar"` is found to be a key to some valid snippet, then `"foo_bar"` and `"#foobar"` won't be searched.

However, this strategy can also be customized easily from the `yas/key-syntaxes` variable. It is a list of syntax rules, the default value is `("w" "w_" "w_." "^ ")`. Which means search the following thing until found one:

- a word.
- a symbol. In lisp, `-` and `?` can all be part of a symbol.
- a sequence of characters of either word, symbol or punctuation.
- a sequence of characters of non-whitespace characters.

But you'd better keep the default value unless you understand what Emacs's syntax rule mean.