In Lisp data objects of type ‘character’ are referred to as characters. For representation purposes, we usually denote character objects by preceding a #\ symbol before the character. Any character can be represented by using the #\ symbol before the name of the character. For Example #\a represents a character ‘a’.
Example 1:
;Lisp Code to print characters (write #\a)
(terpri)(write-char #\a)
(terpri)(write-char #\b)
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Output:
Time Complexity: O(1)
Auxiliary Space: O(1)
Note: “terpri” is a command in Lisp that means “terminate printing” as it is used to terminate a line of output without which the output would be printed in one line.
Special Characters in Lisp:
There are some predefined special characters in Lisp which are:
- #\Backspace
- #\Tab
- #\Page
- #\Linefeed
- #\Return
- #\Rubout
Character Comparison Functions:
In Lisp programming we don’t use numeric comparison functions rather we make use of character comparing functions.
There are two sets of character comparing functions:
- Case-Sensitive Functions: Used when characters are having the same case(lower or upper).
- Case-Insensitive Functions: Used when characters may be having different cases(lower or upper).
| S.No. | Case Sensitive Functions | Case-Insensitive Functions | Description |
|---|---|---|---|
| 1 | char= | char-equal | Checks if operands are equal or not |
| 2 | char/= | char-not-equal | Checks if operands are different or not |
| 3 | char<= | char-not-greaterp | Checks if the value of the left operand is greater than or equal to the value of the next right operand |
| 4 | char>= | char-not-lessp | Checks if the value of the left operand is less than or equal to the value of the next right operand |
| 5 | char< | char-lessp | Checks if the values of the operands are monotonically decreasing or not |
| 6 | char> | char-greaterp | Checks if the values of the operands are monotonically increasing or not |
Note: If in any of the above-mentioned cases the condition in description is satisfied, then it returns ‘T’ else returns ‘NIL’.
Example 2:
;Lisp Case-Sensitive Comparison
(write (char= #\b #\b))
(terpri)(write (char= #\a #\b))
(terpri)(write (char= #\A #\c))
(terpri)(write (char-lessp #\x #\y #\z))
(terpri)(write (char-greaterp #\a #\b #\c))
(terpri) ;Case-Insensitive Comparison
(write (char-equal #\a #\A))
(terpri)(write (char-equal #\a #\b))
(terpri)(write (char-lessp #\x #\y #\z))
(terpri)(write (char-greaterp #\a #\b #\c))
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Output:
Time Complexity: O(1)
Auxiliary Space: O(1)