The Scheme Programming Language

1
The Scheme Programming Language

• History and Significance
• Dmitry Nesvizhsky
• CIS24
• Professor Danny Kopec

2
Scheme History

• Started as an experiment in programming language
  design by challenging some fundamental design
  assumptions
• A dialect of the LISP Programming Language
  invented by Guy Lewis Steele Jr. and Gerald Jay
  Sussman

3
Scheme History

• Emerged from MIT in the mid-1970's
• Originally called Schemer
• Shortened to Scheme because of a 6 character
  limitation on file names
• Designed to have very few regular constructs
  which compose well to support a variety of
  programming styles
• Functional, object-oriented, and imperative

4
Significant Language Features

• Supports lexical scoping, uniform evaluation
  rules, and uniform treatment of data types
• Does not support the concept of a pointer,
  uninitialized variables, specialized looping
  constructs, or explicit storage management
• All data type are equal
• What one can do to one data type, one can do to
  all data types

5
Significant Language Features

• There are seven kinds of expressions
• Constant
• Variable reference
• Procedure creation
• Procedure application
• Conditional
• Assignment
• Sequence

6
Significant Language Features

• Scheme also has the usual assortment of data
  types
• Characters
• Strings
• Arrays
• Lists
• Numbers
• Functions (also called procedures)
• Boolean
• Ports
• Symbols

7
Significant Language Features

• Numbers are especially interesting
• An integer is a rational and a real is a complex
• Scheme requires no looping constructs
• Any function which calls itself in the "tail"
  position is just a loop

8
Significant Language Features

• Scheme has several important advantages
• It is elegantly simple in that regular structure
  and trivial syntax avoids "special case"
  confusion
• Its expressiveness means that one spends little
  time trying to work around the language
• It lets users concentrate on what they want to
  say rather than on how to say it

9
Significant Language Features

• Scheme has several important advantages
  (continued)
• Supports a variety of styles (including
  object-oriented)
• Allows users to better match their solution style
  to the style of the problems to be solved
• Its formal underpinnings make reasoning about
  programs much easier

10
Significant Language Features

• Scheme has several important advantages
  (continued)
• Its abstractive power makes it easy to separate
  system specific optimizations from reusable code
• Its compos ability makes it easy to construct
  systems from well-tested components

11
Areas of Application

• Scheme is currently gaining favor as a first
  programming language in universities and is used
  in industry by such companies as TI, HP, and Sun

12
Areas of Application

• Here are a few statistics regarding the schools
  using Scheme
• 286 colleges/universities worldwide - 108 of
  these use Scheme in introductory courses
• 159 colleges/universities USA only - 49 of these
  use Scheme in introductory courses
• 73 secondary schools worldwide
• 64 secondary schools USA only

13
Sample Program 1

• This program prints the phrase "Hello World
• indigo_at_owlnet.rice.edu (Scott Ruthfield)
• (define hello-world
• (lambda ()
• (begin
• (write Hello-World)
• (newline)
• (hello-world))))

14
Sample Program 2

• Scheme is an imperative language that favors
  recursion over iteration
• The basic data structure is the list
• In Scheme, "car" returns the first element of a
  list and "cdr" returns the remaining elements of
  the list
• There is no need for an "iterator class" or
  pointers, as in C
• In this program cdr recursion is used as an
  iterator, moving from element to element in the
  list
• The result from each recursive call becomes the
  input, or term, for the addition operator, there
  by eliminating the need for a temporary sum
  variable

15
Sample Program 2 (continued)

• List Sum
• This program was found in "An Introduction to
• Scheme" by Jerry Smith, Prentice Hall, 1988
• (define
• (list-sum lst)
• (cond
• ((null? lst) 0)
• ((pair? (car lst))
• ((list-sum (car lst)) (list-sum (cdr lst))))
• (else
• ( (car lst) (list-sum (cdr lst))))))

16
Scheme Performance Table