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)