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In Emacs, a parenthetical grouping at the top level in the buffer is
called a "defun". The name derives from the fact that most top-level
lists in a Lisp file are instances of the special form `defun', but any
top-level parenthetical grouping counts as a defun in Emacs parlance
regardless of what its contents are, and regardless of the programming
language in use. For example, in C, the body of a function definition
is a defun.
Move to beginning of current or preceding defun
Move to end of current or following defun (`end-of-defun').
Put region around whole current or following defun (`mark-defun').
The commands to move to the beginning and end of the current defun
are `C-M-a' (`beginning-of-defun') and `C-M-e' (`end-of-defun').
If you wish to operate on the current defun, use `C-M-h'
(`mark-defun') which puts point at the beginning and mark at the end of
the current or next defun. For example, this is the easiest way to get
ready to move the defun to a different place in the text. In C mode,
`C-M-h' runs the function `mark-c-function', which is almost the same
as `mark-defun'; the difference is that it backs up over the argument
declarations, function name and returned data type so that the entire C
function is inside the region. Note: Marking Objects.
Emacs assumes that any open-parenthesis found in the leftmost column
is the start of a defun. Therefore, *never put an open-parenthesis at
the left margin in a Lisp file unless it is the start of a top level
list. Never put an open-brace or other opening delimiter at the
beginning of a line of C code unless it starts the body of a function.*
The most likely problem case is when you want an opening delimiter at
the start of a line inside a string. To avoid trouble, put an escape
character (`\', in C and Emacs Lisp, `/' in some other Lisp dialects)
before the opening delimiter. It will not affect the contents of the
In the remotest past, the original Emacs found defuns by moving
upward a level of parentheses until there were no more levels to go up.
This always required scanning all the way back to the beginning of the
buffer, even for a small function. To speed up the operation, Emacs
was changed to assume that any `(' (or other character assigned the
syntactic class of opening-delimiter) at the left margin is the start
of a defun. This heuristic is nearly always right and avoids the
costly scan; however, it mandates the convention described above.
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