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ANSI Common Lisp  14 Conses 14.2 Dictionary of Conses
- Syntax:
-
nconc
&rest lists
 concatenated-list
- Arguments and Values:
-
list - each but the last must be a list
(which might be a dotted list but must not be a circular list);
the last list may be any object.
concatenated-list - a list.
- Description:
-
Returns a list that is the concatenation of lists.
If no lists are supplied, (nconc) returns nil.
nconc is defined using the following recursive relationship:
(nconc) ()
(nconc nil . lists) ==(nconc . lists)
(nconc list) list
(nconc list-1 list-2) ==(progn (rplacd (last list-1) list-2) list-1)
(nconc list-1 list-2 . lists) ==(nconc (nconc list-1 list-2) . lists)
- Examples:
-
(nconc) NIL
(setq x '(a b c)) (A B C)
(setq y '(d e f)) (D E F)
(nconc x y) (A B C D E F)
x (A B C D E F)
Note, in the example, that the value of x is now different,
since its last cons
has been rplacd'd to the value of y.
If (nconc x y) were evaluated again,
it would yield a piece of a circular list,
whose printed representation would be
(A B C D E F D E F D E F ...), repeating forever;
if the *print-circle* switch were non-nil,
it would be printed as (A B C . #1=(D E F . #1#)).
(setq foo (list 'a 'b 'c 'd 'e)
bar (list 'f 'g 'h 'i 'j)
baz (list 'k 'l 'm)) (K L M)
(setq foo (nconc foo bar baz)) (A B C D E F G H I J K L M)
foo (A B C D E F G H I J K L M)
bar (F G H I J K L M)
baz (K L M)
(setq foo (list 'a 'b 'c 'd 'e)
bar (list 'f 'g 'h 'i 'j)
baz (list 'k 'l 'm)) (K L M)
(setq foo (nconc nil foo bar nil baz)) (A B C D E F G H I J K L M)
foo (A B C D E F G H I J K L M)
bar (F G H I J K L M)
baz (K L M)
- Side Effects:
-
The lists are modified rather than copied.
?
- See Also:
-
append, concatenate
- Allegro CL Implementation Details:
-
None.
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