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In LISP, variables are not typed, but data objects are.
LISP data types can be categorized as.
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Scalar types − for example, number types, characters, symbols etc.
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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)
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