Editing Common Lisp (section)

===Data structures===
''Sequence'' types in Common Lisp include lists, vectors, bit-vectors, and strings. There are many operations that can work on any sequence type.

As in almost all other Lisp dialects, ''lists'' in Common Lisp are composed of ''conses'', sometimes called ''cons cells'' or ''pairs''. A cons is a data structure with two slots, called its ''car'' and ''cdr''. A list is a linked chain of conses or the empty list. Each cons's car refers to a member of the list (possibly another list). Each cons's cdr refers to the next cons—except for the last cons in a list, whose cdr refers to the <code>nil</code> value. Conses can also easily be used to implement trees and other complex data structures; though it is usually advised to use structure or class instances instead. It is also possible to create circular data structures with conses.

Common Lisp supports multidimensional ''arrays'', and can dynamically resize ''adjustable'' arrays if required. Multidimensional arrays can be used for matrix mathematics. A ''vector'' is a one-dimensional array. Arrays can carry any type as members (even mixed types in the same array) or can be specialized to contain a specific type of members, as in a vector of bits. Usually, only a few types are supported. Many implementations can optimize array functions when the array used is type-specialized. Two type-specialized array types are standard: a ''string'' is a vector of characters, while a ''bit-vector'' is a vector of [[bit]]s.

''[[Hash table]]s'' store associations between data objects. Any object may be used as key or value. Hash tables are automatically resized as needed.

''Packages'' are collections of symbols, used chiefly to separate the parts of a program into [[namespaces]]. A package may ''export'' some symbols, marking them as part of a public interface. Packages can use other packages.

''Structures'', similar in use to [[C (programming language)|C]] structs and [[Pascal (programming language)|Pascal]] records, represent arbitrary complex data structures with any number and type of fields (called ''slots''). Structures allow single-inheritance.

''Classes'' are similar to structures, but offer more dynamic features and multiple-inheritance. (See [[Common Lisp Object System|CLOS]]). Classes have been added late to Common Lisp and there is some conceptual overlap with structures. Objects created of classes are called ''Instances''. A special case is Generic Functions. Generic Functions are both functions and instances.