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