11. Types

Common Lisp is a dynamically and strongly typed language. This means that variables do not have a fixed type, but data types are strictly respected during execution.

Some of the most common data types in Common Lisp are:

• Numbers: integer, float, rational, complex, and number.
• Text strings: character and string.
• Symbols: symbol, keyword, and null.
• Lists: list, cons, and nil.
• Sequences: sequence, vector, and array.
• Hash tables: hash-table, structure-object, and standard-object.
• Functions: function, compiled-function, and generic-function.
• Special: t (true), nil (false or empty list), and boolean.

There are more types, but these are the ones most commonly used.

To check the type of a value, you can use predicates such as typep:

* (typep 42 'integer)
T

* (typep 3.14 'float)
T

* (typep "Hola" 'string)
T

* (typep '(a b c) 'list)
T