Lists as Sets
=============
These functions perform operations on lists which represent sets of
elements.
- Function: member* item list &key :test :test-not :key
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. Note:Sequences.
Note that this function's name is suffixed by `*' to avoid the
incompatible `member' function defined in Emacs. (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.
- Function: tailp sublist list
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.
- Function: adjoin item list &key :test :test-not :key
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.
- Function: union list1 list2 &key :test :test-not :key
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.
- Function: nunion list1 list2 &key :test :test-not :key
This is a destructive version of `union'; rather than copying, it
tries to reuse the storage of the argument lists if possible.
- Function: intersection list1 list2 &key :test :test-not :key
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.
- Function: nintersection list1 list2 &key :test :test-not :key
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.
- Function: set-difference list1 list2 &key :test :test-not :key
This function computes the "set difference" of LIST1 and LIST2,
i.e., the set of elements that appear in LIST1 but _not_ in LIST2.
- Function: nset-difference list1 list2 &key :test :test-not :key
This is a destructive `set-difference', which will try to reuse
LIST1 if possible.
- Function: set-exclusive-or list1 list2 &key :test :test-not :key
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.
- Function: nset-exclusive-or list1 list2 &key :test :test-not :key
This is a destructive `set-exclusive-or', which will try to reuse
LIST1 and LIST2 if possible.
- Function: subsetp list1 list2 &key :test :test-not :key
This function checks whether LIST1 represents a subset of LIST2,
i.e., whether every element of LIST1 also appears in LIST2.