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These functions perform operations on lists which represent sets of elements.
This MacLisp-compatible function searches list for an element
which is equal
to item. The member
function is
built-in to Emacs 19; this package defines it equivalently in Emacs 18.
See the following function for a Common-Lisp compatible version.
This function searches list for an element matching item.
If a match is found, it returns the cons cell whose car
was
the matching element. Otherwise, it returns nil
. Elements
are compared by eql
by default; you can use the :test
,
:test-not
, and :key
arguments to modify this behavior.
See Sequences.
Note that this function’s name is suffixed by ‘*’ to avoid
the incompatible member
function defined in Emacs 19.
(That function uses equal
for comparisons; it is equivalent
to (member* item list :test 'equal)
.)
The member-if
and member-if-not
functions
analogously search for elements which satisfy a given predicate.
This function returns t
if sublist is a sublist of
list, i.e., if sublist is eql
to list or to
any of its cdr
s.
This function conses item onto the front of list,
like (cons item list)
, but only if item
is not already present on the list (as determined by member*
).
If a :key
argument is specified, it is applied to
item as well as to the elements of list during
the search, on the reasoning that item is “about” to
become part of the list.
This function combines two lists which represent sets of items, returning a list that represents the union of those two sets. The result list will contain all items which appear in list1 or list2, and no others. If an item appears in both list1 and list2 it will be copied only once. If an item is duplicated in list1 or list2, it is undefined whether or not that duplication will survive in the result list. The order of elements in the result list is also undefined.
This is a destructive version of union
; rather than copying,
it tries to reuse the storage of the argument lists if possible.
This function computes the intersection of the sets represented by list1 and list2. It returns the list of items which appear in both list1 and list2.
This is a destructive version of intersection
. It
tries to reuse storage of list1 rather than copying.
It does not reuse the storage of list2.
This function computes the “set difference” of list1 and list2, i.e., the set of elements that appear in list1 but not in list2.
This is a destructive set-difference
, which will try
to reuse list1 if possible.
This function computes the “set exclusive or” of list1 and list2, i.e., the set of elements that appear in exactly one of list1 and list2.
This is a destructive set-exclusive-or
, which will try
to reuse list1 and list2 if possible.
This function checks whether list1 represents a subset of list2, i.e., whether every element of list1 also appears in list2.
Next: Association Lists, Previous: Substitution of Expressions, Up: Lists [Contents][Index]