nconc

nconc( 
l_arg1 
l_arg2 
[ l_arg3 ... ] 
) 
=> l_result

Description

Equivalent to a destructive append where the first argument is modified.

This results in nconc being much faster than append but not as fast as tconc and lconc. Thus nconc returns a list consisting of the elements of l_arg1, followed by the elements of l_arg2, followed by the elements of l_arg3, and so on. The cdr of the last list cell of l_arg_i is modified to point to l_arg_i+1. Thus caution must be taken because if nconc is called with the l_arg_i two consecutive times it can form an infinite structure where the cdr of the last list cell of l_arg_i points to the car of l_arg_i.

Use the nconc function principally to reduce the amount of memory consumed. A call to append would normally duplicate the first argument whereas nconc does not duplicate any of its arguments, thereby reducing memory consumption.

Arguments

l_arg1	List of elements.
l_arg2	List elements concatenated to l_arg1.
l_arg3	Additional lists.

Value Returned

l_result

The modified value of l_arg1.

Examples

The following example forms an infinite list structure (a b c d e f g a b c d e f g ...).

x = '(a b c) 
nconc( x '(d))        ; x is now (a b c d)
nconc( x '(e f g) )   ; x is now the list (a b c d e f g)
nconc( x x )          ; Forms an infinite structure.

Related Topics

lconc

tconc

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