LISP - Data Types

In LISP, variables are not typed, but data objects are.
LISP data types can be categorized as.

• Scalar types - for example, number types, characters, symbols etc.
• Data structures - for example, lists, vectors, bit-vectors, and strings.
  

Any variable can take any LISP object as its value, unless you have declared it explicitly.
Although, it is not necessary to specify a data type for a LISP variable, however, it helps in certain loop expansions, in method declarations and some other situations that we will discuss in later chapters.
The data types are arranged into a hierarchy. A data type is a set of LISP objects and many objects may belong to one such set.
The typep predicate is used for finding whether an object belongs to a specific type.
The type-of function returns the data type of a given object.

Type Specifiers in LISP

Type specifiers are system-defined symbols for data types.

array	fixnum	package	simple-string
atom	float	pathname	simple-vector
bignum	function	random-state	single-float
bit	hash-table	ratio	standard-char
bit-vector	integer	rational	stream
character	keyword	readtable	string
[common]	list	sequence	[string-char]
compiled-function	long-float	short-float	symbol
complex	nill	signed-byte	t
cons	null	simple-array	unsigned-byte
double-float	number	simple-bit-vector	vector

Apart from these system-defined types, you can create your own data types. When a structure type is defined using defstruct function, the name of the structure type becomes a valid type symbol.

Example 1

Create new source code file named main.lisp and type the following code in it.

(setq x 10)
(setq y 34.567)
(setq ch nil)
(setq n 123.78)
(setq bg 11.0e+4)
(setq r 124/2)

(print x)
(print y)
(print n)
(print ch)
(print bg)
(print r)

When you click the Execute button, or type Ctrl+E, LISP executes it immediately and the result returned is:

10 
34.567 
123.78 
NIL 
110000.0 
62

Example 2

Next let's check the types of the variables used in the previous example. Create new source code file named main. lisp and type the following code in it.

(defvar x 10)
(defvar y 34.567)
(defvar ch nil)
(defvar n 123.78)
(defvar bg 11.0e+4)
(defvar r 124/2)

(print (type-of x))
(print (type-of y))
(print (type-of n))
(print (type-of ch))
(print (type-of bg))
(print (type-of r))

When you click the Execute button, or type Ctrl+E, LISP executes it immediately and the result returned is:

(INTEGER 0 281474976710655) 
SINGLE-FLOAT 
SINGLE-FLOAT 
NULL 
SINGLE-FLOAT 
(INTEGER 0 281474976710655)