CSI 2120

Lab 10: Scheme

Prerequisites

This lab explores list which will be covered in detail this week. In order to complete the lab, you will need to know:

Scheme uses the same recursive definition of lists as Prolog. What is called the head and tail in Prolog is called the car and cdr in Scheme. (These names come from the original Lisp implementation and stand for "Contents of Address Register" and "Contents of Data Register" referring to some Assembler Macros).
The main function to build lists is the cons function with makes a pair of a car and cdr.
The main function to get at the content of lists are the car and cdr.

Exercise 1: Building Lists

Use cons to build the following lists:


		'(3 4)
		'(1 2 3)
		'(a (b c))
		'(1)
		'(2 (3 (4)))

Exercise 2: List Entries

Use car and cdr to obtain the elements from the list.


;  	Example:
;       (define L '(1 2 3 4 5))    
;
; 	(car L)
; 	=> 1
;
; 	(cdr L)
;       => '(2 3 4 5)
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;

Combine calls car and cdr to get the element 2, 3, 4 and 5 from the list L (4 solutions).


;       (define L '(1 2 3 4 5))    
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;

Combine calls car and cdr to get the element 2 and 5 from the list LL (2 solutions).


;       (define LL '(1 (2 3 4) (5)))    
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;

Note that you can use shorthand commands such


;       (cadr '(1 2))
;       => 2
;       (car (cdr '(1 2)))
;       => 2    
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;

Exercise 3: Integer Range

Give a function that creates a list with integers in the specified range.


;       The function takes two indices, i and k, and produces the integers
;       between i and k including i and k.
;
; 	Example:
; 	(range 4 9)
; 	=> (4 5 6 7 8 9)
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;

Exercise 4 and Quiz: List access

Please hand-in the answer to this question on Virtual Campus during your lab session but at the latest by Friday 6:00pm! Remember, your submission will only count if you have signed the lab attendance sheet.

Give a single function to access the element a in the list Q.

  (define Q '(1 2 (a 3 4 5)))
;;;;;;;;;;;;;;;;;;;;;
; (your_answer Q)      
; => 'a
;;;;;;;;;;;;;;;;;;;