lisp vector

lisp는 기본적으로 list로 하는데
list의 경우 linked list로 내부적으로 구현하기 때문에 아무래도 순차적으로 이동할때 오버헤드가 걸리는데
array에서 파생된 vector는 constant time에 접근이 가능하다고 한다.

One-dimensional arrays are called vectors in Common Lisp and constitute the type vector (which is therefore a subtype of array). Vectors and lists are collectively considered to be sequences. They differ in that any component of a one-dimensional array can be accessed in constant time, whereas the average component access time for a list is linear in the length of the list; on the other hand, adding a new element to the front of a list takes constant time, whereas the same operation on an array takes time linear in the length of the array.

[링크 : http://www.cs.cmu.edu/Groups/AI/html/cltl/clm/node30.html]