Contents
From version 0.6 upwards there are two ways you can quickly find a snippet file. Once you find this file it will be set to snippet-mode (see ahead)
M-x yas/find-snippets
Lets you find the snippet file in the directory the snippet was loaded from (if it exists) like find-file-other-window.
M-x yas/visit-snippet-file
Prompts you for possible snippet expansions like yas/insert-snippet, but instead of expanding it, takes you directly to the snippet definition's file, if it exists.
From version 0.6 upwards there is a major mode snippet-mode to edit snippets. You can set the buffer to this mode with M-x snippet-mode. It provides reasonably useful syntax highlighting.
Two commands are defined in this mode:
M-x yas/load-snippet-buffer
When editing a snippet, this loads the snippet into the correct mode and menu. Bound to C-c C-c by default while in snippet-mode.
M-x yas/tryout-snippet
When editing a snippet, this opens a new empty buffer, sets it to the appropriate major mode and inserts the snippet there, so you can see what it looks like. This is bound to C-c C-t while in snippet-mode.
There are also snippets for making snippets: vars, field and mirror.
The syntax of the snippet template is simple but powerful, very similar to TextMate's.
Arbitrary text can be included as the content of a template. They are usually interpreted as plain text, except $ and `. You need to use \ to escape them: \$ and \`. The \ itself may also needed to be escaped as \\ sometimes.
Elisp code can be embedded inside the template. They are written inside back-quotes (`):
They are evaluated when the snippet is being expanded. The evaluation is done in the same buffer as the snippet being expanded. Here's an example for c-mode to calculate the header file guard dynamically:
#ifndef ${1:_`(upcase (file-name-nondirectory (file-name-sans-extension (buffer-file-name))))`_H_}
#define $1
$0
#endif /* $1 */
From version 0.6.0, snippets expansions are run with some special emacs-lisp variables bound. One of this is yas/selected-text. You can therefore define a snippet like:
for ($1;$2;$3) {
`yas/selected-text`$0
}
to "wrap" the selected region inside your recently inserted snippet. Alternatively, you can also customize the variable yas/wrap-around-region to t which will do this automatically.
Tab stops are fields that you can navigate back and forth by TAB and S-TAB [3]. They are written by $ followed with a number. $0 has the special meaning of the exit point of a snippet. That is the last place to go when you've traveled all the fields. Here's a typical example:
<div$1>
$0
</div>
Tab stops can have default values -- a.k.a placeholders. The syntax is like this:
${N:default value}
They acts as the default value for a tab stop. But when you firstly type at a tab stop, the default value will be replaced by your typing. The number can be omitted if you don't want to create mirrors or transformations for this field.
We refer the tab stops with placeholders as a field. A field can have mirrors. Its mirrors will get updated when you change the text of a field. Here's an example:
\begin{${1:enumerate}}
$0
\end{$1}
When you type "document" at ${1:enumerate}, the word "document" will also be inserted at \end{$1}. The best explanation is to see the screencast(YouTube or avi video).
The tab stops with the same number to the field act as its mirrors. If none of the tab stops has an initial value, the first one is selected as the field and others mirrors.
If the default value of a field starts with $, then it is interpreted as the transformation code instead of default value. A transformation is some arbitrary elisp code that will get evaluated in an environment when the variable text is bind to the inputted text of the field. Here's an example for Objective-C:
- (${1:id})${2:foo}
{
return $2;
}
- (void)set${2:$(capitalize text)}:($1)aValue
{
[$2 autorelease];
$2 = [aValue retain];
}
$0
Look at ${2:$(capitalize text)}, it is a transformation instead of a placeholder. The actual placeholder is at the first line: ${2:foo}. When you type text in ${2:foo}, the transformation will be evaluated and the result will be placed there as the transformated text. So in this example, if you type baz in the field, the transformed text will be Baz. This example is also available in the screencast.
Another example is for rst-mode. In reStructuredText, the document title can be some text surrounded by "===" below and above. The "===" should be at least as long as the text. So
=====
Title
=====
is a valid title but
===
Title
===
is not. Here's an snippet for rst title:
${1:$(make-string (string-width text) ?\=)}
${1:Title}
${1:$(make-string (string-width text) ?\=)}
$0
| [1] | With some minor change, mainly for fixing some trivial bugs. |
| [2] | This is done when you call yas/initialize. |
| [3] | Of course, this can be customized. |
From version 0.6 on, you can also have lisp transformation inside fields. These work mostly mirror transformations but are evaluated when you first enter the field, after each change you make to the field and also just before you exit the field.
The syntax is also a tiny bit different, so that the parser can distinguish between fields and mirrors. In the following example
#define "${1:mydefine$(upcase yas/text)}"
mydefine gets automatically upcased to MYDEFINE once you enter the field. As you type text, it gets filtered through the transformation every time.
Note that this is differentiated from a mirror with a transformation by the existance of extra text between the : and the transformation's $. If you don't want this extra-text, you can use two $'s instead.
#define "${1:$$(upcase yas/text)}"
Please note that as soon as a transformation takes place, it changes the value of the field and sets it its internal modification state to true. As a consequence, the auto-deletion behaviour of normal fields does not take place. This is by design.
As mentioned, the field transformation is invoked just after you enter the field, and with some useful variables bound, notably yas/field-modified-p and yas/moving-away-p. Because of this feature you can place a transformation in the primary field that lets you select default values for it.
The yas/choose-value does this work for you. For example:
<div align="${2:$$(yas/choose-value '("right" "center" "left"))}">
$0
</div>
See the definition of yas/choose-value to see how it was written using the two variables. Also check out yas/verify-value for another neat trick.
From version 0.6 on, you can also have nested placeholders of the type:
<div${1: id="${2:some_id}"}>$0</div>
This allows you to choose if you want to give this div an id attribute. If you tab forward after expanding it will let you change "some_id" to whatever you like. Alternatively, you can just press C-d (which executes yas/skip-and-clear-or-delete-char) and go straight to the exit marker.
By the way, C-d will only clear the field if you cursor is at the beginning of the field and it hasn't been changed yet. Otherwise, it performs the normal Emacs delete-char command.