ANSI Common Lisp 5 Data and Control Flow 5.1 Generalized Reference 5.1.1 Overview of Places and Generalized Reference
220.127.116.11 Evaluation of Subforms to Places
The following rules apply to the evaluation of subforms in a
Rules 2, 3 and 4 cover all standardized macros that manipulate places.
The evaluation ordering of subforms within a place
is determined by the order specified by the second value returned by
For all places defined by this specification
(e.g., getf, ldb, ... ),
this order of evaluation is left-to-right.
When a place is derived from a macro expansion,
this rule is applied after the macro is expanded to find the appropriate place.
Places defined by using defmacro or
use the evaluation order defined by those definitions.
For example, consider the following:
(defmacro wrong-order (x y) `(getf ,y ,x))
This following form evaluates place2 first and
then place1 because that is the order they are evaluated in
the macro expansion:
(push value (wrong-order place1 place2))
For the macros that manipulate places
pop, and those defined by define-modify-macro)
the subforms of the macro call are evaluated exactly once
in left-to-right order, with the subforms of the places
evaluated in the order specified in (1).
push, pushnew, remf,
incf, decf, shiftf, rotatef,
psetf, pop evaluate all subforms before modifying
any of the place locations.
setf (in the case when setf has more than two arguments)
performs its operation on each pair in sequence. For example, in
(setf place1 value1 place2 value2 ...)
the subforms of place1 and value1 are evaluated, the location
place1 is modified to contain the value returned by
then the rest of the setf form is processed in a like manner.
For check-type, ctypecase, and ccase,
subforms of the place are evaluated once as in (1),
but might be evaluated again if the
type check fails in the case of check-type
or none of the cases hold in
ctypecase and ccase.
For assert, the order of evaluation of the generalized
references is not specified.
18.104.22.168.1 Examples of Evaluation of Subforms to Places