Material to Understand

• Structure Declarations. Suppose that a person has a first name, a last name, and an age. Here is how we could declare such a structure.

      (defstruct person   ;; defstruct = DEFine STRUCTure
         first-name
         last-name
         (age 0)          ;; the default value for age is 0
      )
  

• Structure Creation.

     (setf someone (make-person))    
  
           ;; you can give any field name a default value
           ;; when you call the constructor for a structure
     (setf someone-else (make-person :first-name 'Mary))
  

• Field Access.

     (setf (person-first-name someone) 'Joe)
     (setf (person-last-name someone) 'Student)
     (setf (person-age someone) 22)
  

• Other useful predicates.

    (person-p someone)       ;; return t if someone is a person structure
  
    (describe someone)       ;; prints an internal representation
                             ;; of the person instance
  

Exercises

1. Declare a structure called playing-time that can hold the number of minutes and seconds that a song lasts.
2. Instantiate a variable of this structure type and set its minutes to 5 and its seconds to 3.
3. Declare another structure called song that can hold the name of a song and its playing time (which is a structure of the type declared above).
4. Instantiate a variable of this structure type and set its name to Les Copains D'abord and its time to 3 minutes and 5 seconds.
5. Print out the name of the song.
6. Print out the playing time of the song.
7. Declare an array that can contain up to 3 songs.
8. Fill in the array with values of your choosing.
9. Write a function that will print out the contents of this array using format statements.
10. Use the describe function.

Useful Labor Saving Tip from a Former Student

(defun test ( )

  ;; Load the appropriate file, in this case, this one.
  ( load "~account/stuff.l" )

  ;; Do I want tracing on this?
  ( trace factorial )

  ;; Call the desired function with the desired input
  ( factorial 10 )

)