yasnippet/doc/snippet-expansion.org

• Expanding snippets
  • 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
      • Minibuffer prompting
      • Use dropdown-menu.el
      • Roll your own

Expanding snippets

This section describes how YASnippet chooses snippets for expansion at point.

Maybe, you'll want some snippets to be expanded in a particular mode, or only under certain conditions, or be prompted using

Triggering expansion

You can use YASnippet to expand snippets in different ways:

• When yas-minor-mode is active:

  • Type the snippet's trigger key then calling yas-expand (bound to TAB by default).
  • Use the snippet's keybinding.
  • By expanding directly from the "YASnippet" menu in the menu-bar
  • Using hippie-expand
• Call yas-insert-snippet (use M-x yas-insert-snippet= or its keybinding C-c & C-s).
• Use m2m's excellent auto-complete TODO: example for this
• Expanding from emacs-lisp code

Trigger key

yas-expand tries to expand a snippet abbrev (also known as snippet key) before point.

When yas-minor-mode is enabled, it binds yas-expand to TAB and <tab> by default, however, you can freely set it to some other key:

   (define-key yas-minor-mode-map (kbd "<tab>") nil)
   (define-key yas-minor-mode-map (kbd "TAB") nil)
   (define-key yas-minor-mode-map (kbd "<the new key>") 'yas-expand)

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.

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 from you own elisp code. You should call yas-expand-snippet instead of yas-expand in this case.

As with expanding from the menubar, the condition system and multiple candidates doesn't affect expansion. In fact, expanding from the YASnippet menu has the same effect of evaluating the follow code:

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 the current cursor position.

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 the currrent major mode 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 major mode you are in currently.
• Parent tables Snippet tables defined as the parent of some other eligible table are also considered. This works recursively, i.e. parents of parents of eligible tables 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, so using a hook is a good idea.
• Buffer-local yas-buffer-local-condition variable This variable provides finer 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

… 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 through yas-prompt-functions , which defines your preferred methods 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:

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.
• Your window system may or may not allow to you use C-n, C-p to navigate this menu.
• This function can't be used when in a terminal.

Minibuffer prompting

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 the documentation on variable yas-prompt-functions