ELisp: Sequence, Array

What is Sequence Type

• Sequence Type is any of List, Vector, String
• Array Type is any of Vector, String

Here's a hierachy chart of elisp's most important list-like datatypes.

Note: “Sequence” and “Array” are not actual datatypes in elisp. They are grouping names for other actual datatypes.

List and Vector both hold a ordered sequence of values, each value can be any type.

Differences Between List and Vector

Here's the primary differences between List and Vector:

• List, access time to nth element is proportional to size of n.
• List's length can grow by prepending element, and can shorten by removing first element. These operations have constant time.

• Vector, access time to any element is constant.
• Vector's length cannot change. (if you create a new copy of a vector, the time required is proportional to the vector's length)

In short, list can grow or shorten, but if you have a long list, say 1 thousand items, getting the value of 900th item is slow.

Vector has fixed length. Getting the value of any element is fast.