Week 5 comments, questions

Course:  INTRODUCTION TO LISP
instructor:  jgw

ANSWERS to questions assigned
= 8.2 ==============================
Q:8.2 Show how to write ANYODDP using IF instead of COND.

Answer:  (defun anyoddp (x) (if not (null x)) (if (oddp (first (rest 
x)))t)))
[Wrong answer.   Can't figure out how to iterate through a list.]

Book answer:
(defun anyoddp *x)
	(if x
		(if (oddp (first x))
			(first x)
			(anyoddp (rest x)))))
			
Comments:  Is (anyoddp (rest x) the recursive part of the ANYODDP function 
using IF?
========== end 8.2 ==================== 

= 8.4 =================================== 
Q:8.4 Here is a skelton for a LAUGH function:

(defun LAUGH (n)
	(cond (alpha beta)
		      (t (cons 'ha gamma))))
	
Q pt1: Under what condition should the LAUGH function stop recursing?  
Answer: zerop
Q pt2: What value should LAUGH return for that case? 
Answer: ()
Q pt3:  Fill in alpha beta gamma:			  
Answer: 
(defun LAUGH (n) 
     (cond ((zerop n)())
      (t (cons 'HA (LAUGH (- n 1)))))) 
Q pt4:  What happens to LAUGH 0?  
Answer:Empty list is not displayed?
Q pt5:  What happens to LAUGH -1? 
Answer: Doesn't exist with this solution. 
===== end 8.4 ============================

= 8.11 ===================================
Q:8.11 Write a correct version of of the FIB function [allowing for FIB(0) 
and FIB(1)].
Answer:
(defun FIB (n) 
(cond ((equal n 0) 1) ((equal n 1 )1)
	((NOT (equal n 0)  (+ (fib (- n 1))  (fig (-n -2)) ))))

====== end 8.11 ====================

= 8.15 =============================
Q:8.15  Circular list.  What is the CAR and the CDR?  What will the 
COUNT-SLICES function do when given this list as input?

Answer:  The CAR is 'X' the CDR is the CAR.  The COUNT-SLICES function 
will run out of memory.
===== end 8.15 =====================	  
	  



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misc questions -- suggested discussion.
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1) Are sequences just allowed with the COND function or are there any 
other functions that can process sequences?    IF function?  Any others?
---------------------
2) What is the purpose of 'T' in the first three recursive examples of the 
book, chp 8, i.e

   ...(t (ANYODDP (rest x) ...
   ...(t (* n (FACT (-n 1) ...
   ...(t (+ 2 (COUNT-SLICES (rest loaf) ...

   Does calling the name of the functions (ANYODDP, FACT, COUNT-SLICES), 
in these three statements, make the function capable of processing 
sequences?
   ---------------------------
3) Is recursion a part of other distributed programming languages?

   
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comments
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1) From the book "Common Lisp an Interactive Approach" by   Stuart Shapiro
Every recursive function is of the form
 
(defun fn varlist (cond cond-pairs))

 or of the form

   (derfun fn varlist (if test then else))
 
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