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Ch3 Reading Guide 3.1-3.6

Learning Guide

Of course you should read this chapter carefully. It is a quick introduction to the major features of Common Lisp. There are additional sources to read about lightly covered topics:

Questions

  1. Pick what you believe are the three most important of the six “maxims”? List each and give a one sentence example.

  2. What does the function caddar do, anyway?

  3. Why is find preferred over a loop? Give two reasons.

  4. Which two ways are offered for setting variable to a value? Is there a maxim that would apply to help you make the choice? How about overall guidance about using these ways in your program?

Special Forms

  1. List two definitions special forms that you do not know how to use right now.

  2. What do you think the incf and decf special forms do?

  3. Under what circumstances does (defvar x 5) set the variable x to the value 5?

Student

  1. Write the form to define a student structure that contains name, division, id, and an optional home-phone which is set to nil if it is not available.

  2. Create a student with name DocMo, division A321, and id number 666321.

  3. Create a student with your name, division, id number, and a home phone of 773-534-7500.

  4. How can you test to see if a variable v holds a student?

  5. Given the student from two exercises ago, how do you make a list containing just the name and division number.

  6. Set the division of DocMo to 934.

  7. Which is more efficient, storing a list with (name, division, id, home phone) or using a structure? Explain.

Conditionals

  1. What is the most basic special form?

  2. What form should you use to replace (if good-friend nil (run-fast))?

  3. Given an example when the table on page 53 (pdf page 62) does not contain a perfectly accurate translation of the conditional form. Be specific.

  4. Give one way to print a string.

  5. Read the examples using and or or to run conditionals and then write an example that prints out “Go Fish” if the function q19 is called with neither the color 'red nor the suit 'clubs.

    (defun q19 (color suit)
  ...)


20. Which special forms are preferred when the main purpose is to take
    an action? How about returning a value?

21. Given a bunch of tests in a `cond` that all evaluate to
    true, which value should be returned?

22. Suppose you want to perform different actions depending on
    whether an input `dk` is a number or a list. What special form do
    you use?
	
23. Write a function that doubles any number it is given and returns
    only the first element if given a list.

## Repetition

24. What is `mapc`? [Look it
    up](http://www.lispworks.com/documentation/HyperSpec/Body/f_mapc_.htm)
    and summarize.

25. What is the difference between `remove` and `delete`? List a few
    useful variants of `remove`.

26. How do you find the index of an element in a list? Why are there
    two possibilities? 

27. There is an important difference between the `length9` (page 62 /
    PDF 73) and `length10` (page 63 / PDF 74) functions. Carefully
    explain the difference and the implications this difference has
    for the memory usage of the two functions. (**Discuss.**)

## Other

28. What is the value of `(progn 1 2 3)`? 

29. Give an example of a situation where using `progn` is helpful.

30. What is the result of using the `magic` function below in `(magic
    (list 5 10 40 8))`? Explain carefully.

	```lisp
	(defun magic (numbers)
	  (* 3 
		 (let ((ans 5))
		   (dolist (x numbers ans)
			 (if (= x 1)
				 (return 42)
				 (setf ans (* ans x)))))))
	```

## Macros

31. Write what you understand a macro to be, in your own words. If you
    are not sure, write a question or two that you have about macros.
	
32. How do you get one step of expansion of a macro?

## Equality and Sequences (3.4-3.5)

33. There are five main ways to compare items for equality: `=`, `eq`,
    `eql`, `equal`, `equalp`. Briefly explain what each one does and
    how they differ.

34. How is `nth` different from all of the other "getter" functions in
    Section 3.5?
	
35. What is the difference between `assoc` and `rassoc`? 

36. What is a disadvantage of an association list?

37. What more complex data structure can perform the same basic
    function as an association list, but more quickly?
	
## Exercises

1. Do something different depending on the type of an input. Error if
   not one of the choices.
   
2. Truncate a list after the third element. (Note that this is a
   horrible idea.)
   
3. Exercise 3.1, page 56 (PDF page 67).

4. Exercises 3.3 and 3.4, page 70 (PDF page 81): printing an
   expression using dotted pair notation.

5. Write a function that takes in a hash table an a symbol, and
   returns the value from the hash table. Unless the symbol is
   `'DANGER`, in which case it removes the associations for `'MAD` and
   `'ROBOT` from the hash table.