LISP - Characters
In LISP, characters are represented as data objects of type character.
You can denote a character object preceding #\ before the character itself. For example, #\a means the character a.
Space and other special characters can be denoted by preceding #\ before the name of the character. For example, #\SPACE represents the space character.
The following example demonstrates this −
Example
Create a new source code file named main.lisp and type the following code in it.
(write 'a)
(terpri)
(write #\a)
(terpri)
(write-char #\a)
(terpri)
(write-char 'a)
When you execute the code, it returns the following result −
A
#\a
a
*** - WRITE-CHAR: argument A is not a character
Special Characters
Common LISP allows using the following special characters in your code. They are called the semi-standard characters.
- #\Backspace
- #\Tab
- #\Linefeed
- #\Page
- #\Return
- #\Rubout
Character Comparison Functions
Numeric comparison functions and operators, like, < and > do not work on characters. Common LISP provides other two sets of functions for comparing characters in your code.
One set is case-sensitive and the other case-insensitive.
The following table provides the functions −
| Case Sensitive Functions |
Case-insensitive Functions |
Description |
| char= |
char-equal |
Checks if the values of the operands are all equal or not, if yes then condition becomes true. |
| char/= |
char-not-equal |
Checks if the values of the operands are all different or not, if values are not equal then condition becomes true. |
| char< |
char-lessp |
Checks if the values of the operands are monotonically decreasing. |
| char> |
char-greaterp |
Checks if the values of the operands are monotonically increasing. |
| char<= |
char-not-greaterp |
Checks if the value of any left operand is greater than or equal to the value of next right operand, if yes then condition becomes true. |
| char>= |
char-not-lessp |
Checks if the value of any left operand is less than or equal to the value of its right operand, if yes then condition becomes true. |
Example
Create a new source code file named main.lisp and type the following code in it.
; case-sensitive comparison
(write (char= #\a #\b))
(terpri)
(write (char= #\a #\a))
(terpri)
(write (char= #\a #\A))
(terpri)
;case-insensitive comparision
(write (char-equal #\a #\A))
(terpri)
(write (char-equal #\a #\b))
(terpri)
(write (char-lessp #\a #\b #\c))
(terpri)
(write (char-greaterp #\a #\b #\c))
When you execute the code, it returns the following result −
NIL
T
NIL
T
NIL
T
NIL
