code.delx.au - gnu-emacs-elpa/blob - doc/snippet-expansion.org

   1 #+SETUPFILE: org-setup.inc
   2
   3 #+TITLE: Expanding snippets
   4
   5   This section describes how YASnippet chooses snippets for expansion at point.
   6
   7   Maybe, you'll want some snippets to be expanded in a particular
   8   mode, or only under certain conditions, or be prompted using
   9
  10 * Triggering expansion
  11
  12    You can use YASnippet to expand snippets in different ways:
  13
  14    - When [[sym:yas-minor-mode][=yas-minor-mode=]] is active:
  15      - Type the snippet's *trigger key* then calling [[sym:yas-expand][=yas-expand=]]
  16        (bound to =TAB= by default).
  17
  18      - Use the snippet's *keybinding*.
  19
  20      - By expanding directly from the "YASnippet" menu in the menu-bar
  21
  22      - Using hippie-expand
  23
  24    - Call [[sym:yas-insert-snippet][=yas-insert-snippet=]] (use =M-x yas-insert-snippet== or its
  25      keybinding =C-c & C-s=).
  26
  27    - Use m2m's excellent auto-complete
  28      TODO: example for this
  29
  30    - Expanding from emacs-lisp code
  31
  32 ** Trigger key
  33
  34 [[sym:yas-expand][=yas-expand=]] tries to expand a /snippet abbrev/ (also known as
  35 /snippet key/) before point.
  36
  37 When [[sym:yas-minor-mode][=yas-minor-mode=]] is enabled, it binds [[sym:yas-expand][=yas-expand=]] to =TAB= and
  38 =<tab>= by default, however, you can freely set it to some other key:
  39
  40 #+begin_src emacs-lisp :exports code
  41    (define-key yas-minor-mode-map (kbd "<tab>") nil)
  42    (define-key yas-minor-mode-map (kbd "TAB") nil)
  43    (define-key yas-minor-mode-map (kbd "<the new key>") 'yas-expand)
  44 #+end_src
  45
  46 To enable the YASnippet minor mode in all buffers globally use the
  47 command [[sym:yas-global-mode][=yas-global-mode=]]. This will enable a modeline indicator,
  48 =yas=:
  49
  50 [[./images/minor-mode-indicator.png]]
  51
  52 When you use [[sym:yas-global-mode][=yas-global-mode=]] you can also selectively disable
  53 YASnippet in some buffers by setting the buffer-local variable
  54 [[sym:yas-dont-active][=yas-dont-active=]] in the buffer's mode hook.
  55
  56 *** Fallback behaviour
  57
  58 [[sym:yas-fallback-behaviour][=yas-fallback-behaviour=]] is a customization variable bound to
  59 '=call-other-command= by default. If [[sym:yas-expand][=yas-expand=]] failed to find any
  60 suitable snippet to expand, it will disable the minor mode temporarily
  61 and find if there's any other command bound to the same key.
  62
  63 If found, the command will be called. Usually this works very well
  64 --when there's a snippet, expand it, otherwise, call whatever command
  65 originally bind to the trigger key.
  66
  67 However, you can change this behavior by customizing the
  68 [[sym:yas-fallback-behavior][=yas-fallback-behavior=]] variable. If you set this variable to
  69 '=return-nil=, it will return =nil= instead of trying to call the
  70 /original/ command when no snippet is found.
  71
  72 ** Insert at point
  73
  74 The command [[#yas-insert-snippet][=yas-insert-snippet=]] lets you insert snippets at point
  75 /for your current major mode/. It prompts you for the snippet key
  76 first, and then for a snippet template if more than one template
  77 exists for the same key.
  78
  79 The list presented contains the snippets that can be inserted at point,
  80 according to the condition system. If you want to see all applicable
  81 snippets for the major mode, prefix this command with =C-u=.
  82
  83 The prompting methods used are again controlled by
  84 [[sym:yas-prompt-functions][=yas-prompt-functions=]].
  85
  86 ** Snippet keybinding
  87
  88 See the section of the =# binding:= directive in
  89 [[./snippet-development.org][Writing Snippets]].
  90
  91 ** Expanding from the menu
  92
  93 See [[./snippet-menu.org][the YASnippet Menu]].
  94
  95 ** Expanding with =hippie-expand=
  96
  97 To integrate with =hippie-expand=, just put
  98 [[sym:yas-hippie-try-expand][=yas-hippie-try-expand=]] in
  99 =hippie-expand-try-functions-list=. This probably makes more sense
 100 when placed at the top of the list, but it can be put anywhere you
 101 prefer.
 102
 103 ** Expanding from emacs-lisp code
 104
 105 Sometimes you might want to expand a snippet directly from your own
 106 elisp code. You should call [[sym:yas-expand-snippet][=yas-expand-snippet=]] instead of
 107 [[sym:yas-expand][=yas-expand=]] in this case. [[sym:yas-expand-snippet][=yas-expand-snippet=]] takes a string in
 108 snippet template syntax, if you want to expand an existing snippet you
 109 can use [[sym:yas-lookup-snippet][=yas-lookup-snippet=]] to find its contents by name.
 110
 111 As with expanding from the menubar, the condition system and multiple
 112 candidates doesn't affect expansion (the condition system does affect
 113 [[sym:yas-lookup-snippet][=yas-lookup-snippet=]] though). In fact, expanding from the YASnippet
 114 menu has the same effect of evaluating the follow code:
 115
 116 #+BEGIN_SRC emacs-lisp
 117   (yas-expand-snippet template)
 118 #+END_SRC
 119
 120 See the internal documentation on [[sym:yas-expand-snippet][=yas-expand-snippet=]] and
 121 [[sym:yas-lookup-snippet][=yas-lookup-snippet=]] for more information.
 122
 123 * Controlling expansion
 124
 125 ** Eligible snippets
 126
 127 YASnippet does quite a bit of filtering to find out which snippets are
 128 eligible for expanding at the current cursor position.
 129
 130 In particular, the following things matter:
 131
 132 -  Currently loaded snippets tables
 133
 134    These are loaded from a directory hierarchy in your file system. See
 135    [[./snippet-organization.org][Organizing Snippets]]. They are named
 136    after major modes like =html-mode=, =ruby-mode=, etc...
 137
 138 -  Major mode of the current buffer
 139
 140    If the currrent major mode matches one of the loaded snippet tables,
 141    then all that table's snippets are considered for expansion. Use
 142    =M-x describe-variable RET major-mode RET= to find out which major
 143    mode you are in currently.
 144
 145 -  Parent tables
 146
 147    Snippet tables defined as the parent of some other eligible table are
 148    also considered. This works recursively, i.e. parents of parents of
 149    eligible tables are also considered.
 150
 151 -  Buffer-local list of extra modes
 152
 153    Use [[#yas-activate-extra-mode][=yas-activate-extra-mode=]] to
 154    consider snippet tables whose name does not correspond to a major
 155    mode. Typically, you call this from a minor mode hook, for example:
 156
 157 #+BEGIN_SRC emacs-lisp
 158   ;; When entering rinari-minor-mode, consider also the snippets in the
 159   ;; snippet table "rails-mode"
 160   (add-hook 'rinari-minor-mode-hook
 161             #'(lambda ()
 162                 (yas-activate-extra-mode 'rails-mode)))
 163 #+END_SRC
 164
 165 -  Buffer-local
 166    [[sym:yas-buffer-local-condition][=yas-buffer-local-condition=]]
 167    variable
 168
 169    This variable provides finer grained control over what snippets can
 170    be expanded in the current buffer. The default value won't let you
 171    expand snippets inside comments or string literals for example. See
 172    The condition system\_ for more info.
 173
 174 ** The condition system
 175
 176 Consider this scenario: you are an old Emacs hacker. You like the
 177 abbrev-way and bind [[sym:yas-expand][=yas-expand=]] to =SPC=. However, you don't want
 178 =if= to be expanded as a snippet when you are typing in a comment
 179 block or a string (e.g. in =python-mode=).
 180
 181 If you use the =# condition := directive (see
 182 [[./snippet-development.org][Writing Snippets]]) you could just specify
 183 the condition for =if= to be =(not (python-in-string/comment))=. But how
 184 about =while=, =for=, etc. ? Writing the same condition for all the
 185 snippets is just boring. So has a buffer local variable
 186 [[sym:yas-buffer-local-condition][=yas-buffer-local-condition=]]. You can set this variable to
 187 =(not (python-in-string/comment))= in =python-mode-hook=.
 188
 189 Then, what if you really want some particular snippet to expand even
 190 inside a comment? Set [[sym:yas-buffer-local-condition][=yas-buffer-local-condition=]] like this
 191
 192 #+BEGIN_SRC emacs-lisp
 193   (add-hook 'python-mode-hook
 194             (lambda ()
 195               (setq yas-buffer-local-condition
 196                     '(if (python-in-string/comment)
 197                          '(require-snippet-condition . force-in-comment)
 198                        t))))
 199 #+END_SRC
 200
 201 ... and specify the condition for a snippet that you're going to expand
 202 in comment to be evaluated to the symbol =force-in-comment=. Then it can
 203 be expanded as you expected, while other snippets like =if= still can't
 204 expanded in comment.
 205
 206 For the full set of possible conditions, see the documentation for
 207 [[sym:yas-buffer-local-condition][=yas-buffer-local-condition=]].
 208
 209 ** Multiples snippet with the same key
 210
 211 The rules outlined [[Eligible%20snippets][above]] can return more than
 212 one snippet to be expanded at point.
 213
 214 When there are multiple candidates, YASnippet will let you select one.
 215 The UI for selecting multiple candidate can be customized through
 216 [[sym:yas-prompt-functions][=yas-prompt-functions=]] , which defines your preferred methods of being
 217 prompted for snippets.
 218
 219 You can customize it with
 220 =M-x customize-variable RET yas-prompt-functions RET=. Alternatively you
 221 can put in your emacs-file:
 222
 223 #+BEGIN_SRC emacs-lisp
 224   (setq yas-prompt-functions '(yas-x-prompt yas-dropdown-prompt))
 225 #+END_SRC
 226
 227 Currently there are some alternatives solution with YASnippet.
 228
 229 *** Use the X window system
 230
 231 [[./images/x-menu.png]]
 232
 233 The function [[sym:yas-x-prompt][=yas-x-prompt=]] can be used to show a popup menu for you to
 234 select. This menu will be part of you native window system widget, which
 235 means:
 236
 237 -  It usually looks beautiful. E.g. when you compile Emacs with gtk
 238    support, this menu will be rendered with your gtk theme.
 239 -  Your window system may or may not allow to you use =C-n=, =C-p= to
 240    navigate this menu.
 241 -  This function can't be used when in a terminal.
 242
 243 *** Minibuffer prompting
 244
 245 [[./images/ido-menu.png]]
 246
 247 You can use functions [[sym:yas-completing-prompt][=yas-completing-prompt=]] for the classic emacs
 248 completion method or [[sym:yas-ido-prompt][=yas-ido-prompt=]] for a much nicer looking method.
 249 The best way is to try it. This works in a terminal.
 250
 251 *** Use =dropdown-menu.el=
 252
 253 [[./images/dropdown-menu.png]]
 254
 255 The function [[sym:yas-dropdown-prompt][=yas-dropdown-prompt=]] can also be placed in the
 256 [[sym:yas-prompt-functions][=yas-prompt-functions=]] list.
 257
 258 This works in both window system and terminal and is customizable, you
 259 can use =C-n=, =C-p= to navigate, =q= to quit and even press =6= as a
 260 shortcut to select the 6th candidate.
 261
 262 *** Roll your own
 263
 264 See the documentation on variable [[sym:yas-prompt-functions][=yas-prompt-functions=]]