Logical functions

1
Logical functions

• and - Logical AND function. Example
• (and (gt 5 4) (lt 5 4))
• or - Logical OR function. Example
• (and (gt 5 4) (lt 5 4))
• not - Logical negation. Example
• (not (gt 5 4))

2
Conditionals - when, unless

• (when condition statements)
• (when t (print true))
• (when nil (print true))
• (unless condition statements)
• (unless t (print true))
• (unless nil (print true))

3
Conditionals - cond

• COND - This is similar to the familiar switch
  construct that you have encountered. Here is the
  syntax
• (cond (cond1 command1)
• (cond1 command2)
• )

4
Conditionals - cond

• Example of COND in use
• (setq a 3)
• (cond
• ((evenp a) a) if a is even, return a
• ((gt a 7) (/ a 2))
• ((lt a 5) ( a 1))
• (t 1000)
• )

5
Conditionals - case

• The LISP case statement is similar to that of
  Cs. For example
• (setq greeting n)
• (case greeting
• (m Good morning)
• (e Good evening)
• (n Good nite)
• )

6
Program block - progn

• Sometimes we may need to use more than one
  statement within the then and/or the else clause
  of an if statement.
• To achieve this, use the progn construct. For
  example
• (if (gt a 5)
• (progn
• (setq a ( b 7))
• (setq b ( c 8)))
• (setq b 4)) the else clause

The then clause