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, psts, vectors, bit-vectors, and strings.

Any variable can take any LISP object as its value, unless you have declared it exppcitly.

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.

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 vapd type symbol.

Example 1

Create new source code file named main.psp 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)

10 
34.567 
123.78 
NIL 
110000.0 
62

(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))

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