This package defines a number of macros that operate on generalized variables. Many are interesting and useful even when the place is just a variable name.
This macro is to
setq: When several places and forms are involved, the assignments take place in parallel rather than sequentially. Specifically, all subforms are evaluated from left to right, then all the assignments are done (in an undefined order).
This macro increments the number stored in place by one, or by x if specified. The incremented value is returned. For example,
(cl-incf i)is equivalent to
(setq i (1+ i)), and
(cl-incf (car x) 2)is equivalent to
(setcar x (+ (car x) 2)).
setf, care is taken to preserve the “apparent” order of evaluation. For example,(cl-incf (aref vec (cl-incf i)))
appears to increment
ionce, then increment the element of
i; this is indeed exactly what it does, which means the above form is not equivalent to the “obvious” expansion,(setf (aref vec (cl-incf i)) (1+ (aref vec (cl-incf i)))) ; wrong!
but rather to something more like(let ((temp (cl-incf i))) (setf (aref vec temp) (1+ (aref vec temp))))
Again, all of this is taken care of automatically by
cl-incfand the other generalized-variable macros.
As a more Emacs-specific example of
cl-incf, the expression
)is essentially equivalent to
This macro decrements the number stored in place by one, or by x if specified.
This macro inserts x at the front of the list stored in place, but only if x was not
eqlto any existing element of the list. The optional keyword arguments are interpreted in the same way as for
cl-adjoin. See Lists as Sets.
This macro shifts the places left by one, shifting in the value of newvalue (which may be any Lisp expression, not just a generalized variable), and returning the value shifted out of the first place. Thus,
(cl-shiftfa b c d
)is equivalent to(prog1 a (cl-psetf a b b c c d))
except that the subforms of a, b, and c are actually evaluated only once each and in the apparent order.
This macro rotates the places left by one in circular fashion. Thus,
(cl-rotatefa b c d
)is equivalent to(cl-psetf a b b c c d d a)
except for the evaluation of subforms.
nil. Note that
)conveniently exchanges a and b.
The following macros were invented for this package; they have no analogues in Common Lisp.
This macro is analogous to
let, but for generalized variables rather than just symbols. Each binding should be of the form
); the original contents of the places are saved, the values are stored in them, and then the body forms are executed. Afterwards, the places are set back to their original saved contents. This cleanup happens even if the forms exit irregularly due to a
throwor an error.
For example,(cl-letf (((point) (point-min)) (a 17)) ...)
moves point in the current buffer to the beginning of the buffer, and also binds
ato 17 (as if by a normal
ais just a regular variable). After the body exits,
ais set back to its original value and point is moved back to its original position.
(point)is not quite like a
save-excursion, as the latter effectively saves a marker which tracks insertions and deletions in the buffer. Actually, a
(point-marker)is much closer to this behavior. (
point-markerare equivalent as
setfplaces; each will accept either an integer or a marker as the stored value.)
Since generalized variables look like lists,
let's shorthand of using ‘foo’ for ‘(foo nil)’ as a binding would be ambiguous in
cl-letfand is not allowed.
However, a binding specifier may be a one-element list ‘(place)’, which is similar to ‘(place place)’. In other words, the place is not disturbed on entry to the body, and the only effect of the
cl-letfis to restore the original value of place afterwards.
Note that in this case, and in fact almost every case, place must have a well-defined value outside the
cl-letfbody. There is essentially only one exception to this, which is place a plain variable with a specified value (such as
(a 17)in the above example).
Note that the cl.el version of this macro behaves slightly differently. See Obsolete Macros.
This macro is to
let: It does the bindings in sequential rather than parallel order.
This is the “generic” modify macro. It calls function, which should be an unquoted function name, macro name, or lambda. It passes place and args as arguments, and assigns the result back to place. For example,
)is the same as
(cl-callf +place n
). Some more examples:(cl-callf abs my-number) (cl-callf concat (buffer-name) "<" (number-to-string n) ">") (cl-callf cl-union happy-people (list joe bob) :test 'same-person)
Note again that
cl-callfis an extension to standard Common Lisp.
This macro is like
cl-callf, except that place is the second argument of function rather than the first. For example,
)is equivalent to
(cl-callf2 consx place
cl-callf2 macros serve as building
blocks for other macros like
cl-letf* macros are used in the processing
of symbol macros; see Macro Bindings.