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)
