Material to Understand

• The atom t represents true.
• nil and () and '() are equivalent and represent false.
• Anything that is not nil also represents true.
• The predicate =. Example: (= 4 4)
• The predicate eq. Example: (eq 'apple 'orange)
• The predicate equal. Example: (equal '(1 2) '(1 2))
• The predicate member. Example: (member 2 '(1 2 3))
• Keyword arguments.

       (member '(1 2) '((1 1)(1 2)(1 3)))
                    versus
       (member '(1 2) '((1 1)(1 2)(1 3)) :test #'equal)
  

• The predicate listp.
• The predicate atom.
• The predicate numberp.
• The predicate symbolp.
• The predicate null.
• The predicate endp.
• The predicates >, <, >=, <=.
• The boolean operators and, or, not. Example: (and t nil t)
• The conditional if. The else part is optional.

     (if (> a b)    ;; condition, a and b must have values
         (+ a 1)    ;; do this ONE statement if true
         (+ b 1)    ;; do this ONE statement if false
     )
  

• The conditional cond. This statement is equivalent to an if-elseif-elseif-etc construct.

     (cond 
       ( test1  statement-1 ... statement-n )  
       ( test2  statement-1 ... statement-m )
          ...
       ( testk  statement-1 ... statement-p )
     )
  
     (cond
       ((> temp 80) 'hot)
       ((> temp 60) 'warm)
       (t  'cool-or-cold)
     )
  

• The conditional case.

    (case temperature 
      (100 'hot)
      (99 'hot)
       ...
      (otherwise 'unknown)
    )
  

Exercises

1. Demonstrate a case where equal and eq return different results.
2. Demonstrate a case where equal and = return different results.
3. Use Clisp to determine whether 4 is an atom, a number, a symbol, and a list.
4. Repeat question 3 for nil. Do you understand your results?
5. Use Clisp to determine whether the numbers in '(2 3 4) are in ascending order.
6. Explain the results of (not nil), (and (< 2 3) (evenp 6)), (or nil t nil), and (not '(1 2 3)).
7. Write a function called compare that takes arguments a and b. The function should return the larger of the two values using an if statement.
8. Write a function called compare-and-add that takes no arguments and uses a cond statement to compare the values stored in variables a and b. If a is larger, add one to the value of a and then return this value. If b is larger, add one to the value of b and then return this value. If they are equal, return the atom 'same. Test out your function to make sure that it is working properly.
9. What happens if you try to use an if statement to solve question 8?
10. Use the member function to show that '(cs425 starkey) is present in the list '((cs436 paxton)(cs425 starkey)(cs440 harkin)).
11. (Problem 4-7.) Define check-temperature, a procedure that is to take one argument, such that it returns ridiculously-hot if the argument is greater than 100, ridiculously-cold if the argument is less than 0, and OK otherwise.