Assignment 1

• equalp, eql
• length
• 1+, 1-
• abs
• elt, nth
• first, second, third, cadr, rest
• integerp - hack, always returns true

• setf replaced with setq

 Problem 1:
 1. (third (the quick brown fox))
  ERROR: Too many arguments.  Error signalled by THE.
  CAUSE: Missing quote in front of list
  SOLUTION:

 2. (list 2 and 2 is 4)
  ERROR: The variable AND is unbound.
  CAUSE: Missing quote around 'and' and 'is'
  SOLUTION: 

 3. (cdr (car '(a b c)))
  ERROR: A is not of type LIST.  Error signalled by CDR.
       CAUSE: cdr needs a list as input
       SOLUTION: 

 4.  (+ 1 '(length (list t t t t)))
  ERROR: (LENGTH (LIST T T ...)) is not of type NUMBER.
  CAUSE: Unnecessary quote before 'length' function.
  SOLUTION: 

 5. (evenp (+ 4.0 2.0))
  ERROR: 6.0 is not of type INTEGER.
  CAUSE: evenp requires parameters to be integers.
  SOLUTION: 

 6. (cons 'mary (betty carolyn))
  ERROR: The function BETTY is undefined.
  CAUSE: Missing quote in front of list.
  SOLUTION: 

 7. (append '(a b c) 'd)
  ERROR: No error, just incorrect answer (A B C .D)
  CAUSE: Missing brackets around 'd': append really wants 2 lists
  SOLUTION: 

 8. (cons 'mary (list betty carolyn))
  ERROR: The variable BETTY is unbound.
  CAUSE: Missing quotes in front of atoms
  SOLUTION:  

 9. (1+ '(cdr (2 3 4)))
  ERROR: (CDR (2 3 4)) is not of type NUMBER.
  CAUSE: The function 1+ cannot increment elements of a list b iteself
  SOLUTION: 

 10.   (setq x length (a b c))
  ERROR: The variable LENGTH is unbound.
  CAUSE: Missing backets around length and quote around list
  SOLUTION: 

 PROBLEM 2, Question 1.
 Function Name :   sub20
 Description   :   Takes a number, subtracts 20 from it, and returns the result.

 PROBLEM 2, Question 2.
 Function Name : square50-
 Description   : Returns the square of its argument iff its argument is a
     positive integer less than or equal to 50. Else returns nil.

 solution using cond

 solution using if

 PROBLEM 3
 Function Name : constrain
 Description   : If x is less than or equal to minarg, minarg is returned.
       If x is greater than or equal to maxarg, maxarg is returned.
       Otherwise x is returned.
 Notes     : As the name implies the implementation uses the conditional
      construct.
       The specification does not explicitly state the
      arguments are numbers but the use of < and > operators implies
      so.

 Variant Problem 3:
 Function name : constrain-if
 Description   : as for constrain above.
 Notes         : As for constrain-if above except that as the name implies
     this implementation uses the if construct.

 PROBLEM 4
 Function name : precede
 Description   : Given an integer x and a list l as arguments, a list of all
      the items immediately preceding x in the list l is returned.
 Notes         : This implementation is recursive.
                 Does not check any sublists

 version using cond

 version using if

 variant of PROBLEM 4
 Function Name : precede-iter
 Description   : As for precede above.
 Notes     : As the name implies this implementation is iterative.

 check - this may not be correct

 PROBLEM 5
 Function Name :  Intersperse
 Description   :  Takes an object o and a list l as arguments and returns a new;       list in which the object appears between every pair of elements
       in the original list.
 Notes     :  This is a recursive implementation.

 variant PROBLEM 5
 Function Name : Intersperse-Iter
 Description   : As for Intersperse above.
 Notes     : This is an iterative implementation.

 Problem 6

 recursive and iterative versions of a function which returns true
 iff the difference between every successive pair of elements is 1.