code.delx.au - gnu-emacs-elpa/blob - packages/yasnippet/doc/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 you own
 106 elisp code. You should call
 107 [[sym:yas-expand-snippet][=yas-expand-snippet=]] instead of
 108 [[sym:yas-expand][=yas-expand=]] in this case.
 109
 110 As with expanding from the menubar, the condition system and multiple
 111 candidates doesn't affect expansion. In fact, expanding from the
 112 YASnippet menu has the same effect of evaluating the follow code:
 113
 114 #+BEGIN_SRC emacs-lisp
 115   (yas-expand-snippet template)
 116 #+END_SRC
 117
 118 See the internal documentation on [[sym:yas-expand-snippet][=yas-expand-snippet=]] for more
 119 information.
 120
 121 * Controlling expansion
 122
 123 ** Eligible snippets
 124
 125 YASnippet does quite a bit of filtering to find out which snippets are
 126 eligible for expanding at the current cursor position.
 127
 128 In particular, the following things matter:
 129
 130 -  Currently loaded snippets tables
 131
 132    These are loaded from a directory hierarchy in your file system. See
 133    [[./snippet-organization.org][Organizing Snippets]]. They are named
 134    after major modes like =html-mode=, =ruby-mode=, etc...
 135
 136 -  Major mode of the current buffer
 137
 138    If the currrent major mode matches one of the loaded snippet tables,
 139    then all that table's snippets are considered for expansion. Use
 140    =M-x describe-variable RET major-mode RET= to find out which major
 141    mode you are in currently.
 142
 143 -  Parent tables
 144
 145    Snippet tables defined as the parent of some other eligible table are
 146    also considered. This works recursively, i.e. parents of parents of
 147    eligible tables are also considered.
 148
 149 -  Buffer-local list of extra modes
 150
 151    Use [[#yas-activate-extra-mode][=yas-activate-extra-mode=]] to
 152    consider snippet tables whose name does not correspond to a major
 153    mode. Typically, you call this from a minor mode hook, for example:
 154
 155 #+BEGIN_SRC emacs-lisp
 156   ;; When entering rinari-minor-mode, consider also the snippets in the
 157   ;; snippet table "rails-mode"
 158   (add-hook 'rinari-minor-mode-hook
 159             #'(lambda ()
 160                 (yas-activate-extra-mode 'rails-mode)))
 161 #+END_SRC
 162
 163 -  Buffer-local
 164    [[sym:yas-buffer-local-condition][=yas-buffer-local-condition=]]
 165    variable
 166
 167    This variable provides finer grained control over what snippets can
 168    be expanded in the current buffer. The default value won't let you
 169    expand snippets inside comments or string literals for example. See
 170    The condition system\_ for more info.
 171
 172 ** The condition system
 173
 174 Consider this scenario: you are an old Emacs hacker. You like the
 175 abbrev-way and bind [[sym:yas-expand][=yas-expand=]] to =SPC=. However, you don't want
 176 =if= to be expanded as a snippet when you are typing in a comment
 177 block or a string (e.g. in =python-mode=).
 178
 179 If you use the =# condition := directive (see
 180 [[./snippet-development.org][Writing Snippets]]) you could just specify
 181 the condition for =if= to be =(not (python-in-string/comment))=. But how
 182 about =while=, =for=, etc. ? Writing the same condition for all the
 183 snippets is just boring. So has a buffer local variable
 184 [[sym:yas-buffer-local-condition][=yas-buffer-local-condition=]]. You can set this variable to
 185 =(not (python-in-string/comment))= in =python-mode-hook=.
 186
 187 Then, what if you really want some particular snippet to expand even
 188 inside a comment? Set [[sym:yas-buffer-local-condition][=yas-buffer-local-condition=]] like this
 189
 190 #+BEGIN_SRC emacs-lisp
 191   (add-hook 'python-mode-hook
 192             (lambda ()
 193               (setq yas-buffer-local-condition
 194                     '(if (python-in-string/comment)
 195                          '(require-snippet-condition . force-in-comment)
 196                        t))))
 197 #+END_SRC
 198
 199 ... and specify the condition for a snippet that you're going to expand
 200 in comment to be evaluated to the symbol =force-in-comment=. Then it can
 201 be expanded as you expected, while other snippets like =if= still can't
 202 expanded in comment.
 203
 204 For the full set of possible conditions, see the documentation for
 205 [[sym:yas-buffer-local-condition][=yas-buffer-local-condition=]].
 206
 207 ** Multiples snippet with the same key
 208
 209 The rules outlined [[Eligible%20snippets][above]] can return more than
 210 one snippet to be expanded at point.
 211
 212 When there are multiple candidates, YASnippet will let you select one.
 213 The UI for selecting multiple candidate can be customized through
 214 [[sym:yas-prompt-functions][=yas-prompt-functions=]] , which defines your preferred methods of being
 215 prompted for snippets.
 216
 217 You can customize it with
 218 =M-x customize-variable RET yas-prompt-functions RET=. Alternatively you
 219 can put in your emacs-file:
 220
 221 #+BEGIN_SRC emacs-lisp
 222   (setq yas-prompt-functions '(yas-x-prompt yas-dropdown-prompt))
 223 #+END_SRC
 224
 225 Currently there are some alternatives solution with YASnippet.
 226
 227 *** Use the X window system
 228
 229 [[./images/x-menu.png]]
 230
 231 The function [[sym:yas-x-prompt][=yas-x-prompt=]] can be used to show a popup menu for you to
 232 select. This menu will be part of you native window system widget, which
 233 means:
 234
 235 -  It usually looks beautiful. E.g. when you compile Emacs with gtk
 236    support, this menu will be rendered with your gtk theme.
 237 -  Your window system may or may not allow to you use =C-n=, =C-p= to
 238    navigate this menu.
 239 -  This function can't be used when in a terminal.
 240
 241 *** Minibuffer prompting
 242
 243 [[./images/ido-menu.png]]
 244
 245 You can use functions [[sym:yas-completing-prompt][=yas-completing-prompt=]] for the classic emacs
 246 completion method or [[sym:yas-ido-prompt][=yas-ido-prompt=]] for a much nicer looking method.
 247 The best way is to try it. This works in a terminal.
 248
 249 *** Use =dropdown-menu.el=
 250
 251 [[./images/dropdown-menu.png]]
 252
 253 The function [[sym:yas-dropdown-prompt][=yas-dropdown-prompt=]] can also be placed in the
 254 [[sym:yas-prompt-functions][=yas-prompt-functions=]] list.
 255
 256 This works in both window system and terminal and is customizable, you
 257 can use =C-n=, =C-p= to navigate, =q= to quit and even press =6= as a
 258 shortcut to select the 6th candidate.
 259
 260 *** Roll your own
 261
 262 See the documentation on variable [[sym:yas-prompt-functions][=yas-prompt-functions=]]