Major Section: PROGRAMMING
General Forms: (set-difference$ l1 l2) (set-difference$ l1 l2 :test 'eql) ; same as above (eql as equality test) (set-difference$ l1 l2 :test 'eq) ; same, but eq is equality test (set-difference$ l1 l2 :test 'equal) ; same, but equal is equality test
(Set-difference$ l1 l2)
equals a list that contains the member
s of
x
that are not member
s of y
. More precisely, the resulting
list is the same as one gets by deleting the members of y
from x
,
leaving the remaining elements in the same order as in x
. The optional
keyword, :TEST
, has no effect logically, but provides the test (default
eql
) used for comparing members of the two lists.
The guard for a call of set-difference$
depends on the test. In all
cases, both arguments must satisfy true-listp
. If the test is
eql
, then one of the arguments must satisfy eqlable-listp
. If
the test is eq
, then one of the arguments must satisfy
symbol-listp
.
See equality-variants for a discussion of the relation between
set-difference$
and its variants:
(set-difference-eq x lst)
is equivalent to(set-difference$ x lst :test 'eq)
;
(set-difference-equal x lst)
is equivalent to(set-difference$ x lst :test 'equal)
.
In particular, reasoning about any of these primitives reduces to reasoning
about the function set-difference-equal
.
Set-difference$
is similar to the Common Lisp primitive
set-difference
. However, Common Lisp does not specify the order of
elements in the result of a call of set-difference
.