setf is a modest name for a macro that does much more work than it
gets paid for. Quoting the doc page:
This is a generalized version of `setq'; the PLACEs may be symbolic
references such as (car x) or (aref x i), as well as plain symbols.
For example, (setf (cadr x) y) is equivalent to (setcar (cdr x) y).
The return value is the last VAL in the list.
Upon reading that, you'd be excused for thinking something mediocre
such as “That's neat!” or “I'll try to remember that”. That
understatement of a doc page merely touches on the power that lies
beneath the surface.
Let's start with an example from the manual, depending on your Emacs
version you may need to (require 'cl) first.
(let((world"world"))(setf(substringworld24)"o"));; world is now "wood"
Now say you want to replace the entire contents of a buffer, instead
of the manual erase-buffer then insert, you could do
(setf(buffer-string)"replacement")
Let's get slightly more practical. Do you know which function changes
the buffer being displayed by a given window? How about changing the
height of a window? You don't need to!
The ins and outs of setf
24 Aug 2014, by Artur Malabarba.Common-Lisp in Emacs post series
setfis a modest name for a macro that does much more work than it gets paid for. Quoting the doc page:Upon reading that, you'd be excused for thinking something mediocre such as “That's neat!” or “I'll try to remember that”. That understatement of a doc page merely touches on the power that lies beneath the surface.
Let's start with an example from the manual, depending on your Emacs version you may need to
(require 'cl)first.Now say you want to replace the entire contents of a buffer, instead of the manual
erase-buffertheninsert, you could doLet's get slightly more practical. Do you know which function changes the buffer being displayed by a given window? How about changing the height of a window? You don't need to!
And finally, if we just want to get cute,
For a wider list, have a look at cl package manual page, which lists what you get by requiring
clorcl-lib, or see the elisp manual page, which lists what's loaded by default on recent versions of Emacs. My thanks to Christopher Wellons and Rob Thorpe for the links, and it was Wellons' post on string mutability which inspired this post.Tags: lisp, emacs,
Understanding letf and how it replaces flet »
« Meta Binds Part 3: Smart string insertion
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